UNIVERSIDAD DE INVESTIGACION DE

UNIVERSIDAD DE INVESTIGACION DETECNOLOGIA EXPERIMENTAL

YACHAY

Escuela de Ciencias Quımicas e Ingenierıa

TITULO: Characterization of Painting Components

in Ecuadorian Artworks of 17thCentury by

Vibrational Spectroscopy

Trabajo de integracion curricular presentado como requisito para

la obtencion del tıtulo de Quımico/a

Autor:

Anchalı Guamanquispe Sophıa Nicole

Tutores:

M.Sc. De Lima Eljuri Lola Marıa

Ph.D. Palma Cando Alex Uriel

Co-Tutor:

M.Sc. Vasquez Mora Carlos Andres

Urcuquı, febrero 2021

Autorıa

Yo, SOPHIA NICOLE ANCHALI GUAMANQUISPE, con cedula de identidad

1803987005, declaro que las ideas, juicios, valoraciones, interpretaciones, consultas biblio-

graficas, definiciones y conceptualizaciones expuestas en el presente trabajo; ası como,

los procedimientos y herramientas utilizadas en la investigacion, son de absoluta respon-

sabilidad de el/la autor(a) del trabajo de integracion curricular. Ası mismo, me acojo a

los reglamentos internos de la Universidad de Investigacion de Tecnologıa Experimental

Yachay.

Urcuquı, febrero 2021.

Sophıa Nicole Anchalı Guamanquispe

C.I. 1803987005

Autorizacion de Publicacion

Yo, SOPHIA NICOLE ANCHALI GUAMANQUISPE, con cedula de identidad

1803987005, cedo a la Universidad de Investigacion de Tecnologıa Experimental Yachay,

los derechos de publicacion de la presente obra, sin que deba haber un reconocimiento

economico por este concepto. Declaro ademas que el texto del presente trabajo de titu-

lacion no podra ser cedido a ninguna empresa editorial para su publicacion u otros fines,

sin contar previamente con la autorizacion escrita de la Universidad.

Asimismo, autorizo a la Universidad que realice la digitalizacion y publicacion de este

trabajo de integracion curricular en el repositorio virtual, de conformidad a lo dispuesto

en el Art. 144 de la Ley Organica de Educacion Superior.

Urcuquı, febrero 2021.

Sophıa Nicole Anchalı Guamanquispe

C.I. 1803987005

To my lovely parents Amparito & Luis

for their love, care, and unconditional support.

To my dear grandparents Carmen†, Anibal, and Charito

for their eternal love and blessings.

Acknowledgments

First, I want to express my deep gratitude to my parents, Amparito Guamanquispe and

Luis Anchalı, for their love and discipline to guide me in the right way. To my grandpar-

ents, for their blessings, without which I would not be here. To all my aunts who have

been like second mothers and sisters. To my little hearts, for their inspiring smiles, my

cousins and my sister.

I want to thank my boyfriend Jhon for his unconditional love and for always have the

right words to motivate me to follow all my dreams. I thank my best friend, Joss, for

all her support and inevitable laughs. Also, I thank my special friend, Fer, who help me

enormously in this process.

I extend my gratefulness to my alma mater, Yachay Tech University, for the experiences

lived and the acquired knowledge. To all my professors, who were fundamental in each

part of my academic training.

I want to give a special acknowledgment to my advisor, Lola De Lima M.Sc., for her

valuable guidance and goodwill during this extensive process. To Manuel Caetano Ph.D.,

and his daughter Gaby, for all their recommendations. I also want to thank Alex Palma

Ph.D., my second advisor, who allowed me to work on this topic.

I thank from the heart my Professors Marta, Vivian, Hortensia, and Lilian for their knowl-

edge and friendship.

I thank the Instituto Nacional de Patrimonio Cultural (INPC) for opening the doors

to me, especially those who are part of the Investigation Department, Martha Romero

Ph.D., Carlos Vasquez M.Sc., Chem. Michelle Marmol, Restorer Fernando Espinoza and

Restorer Edgar Santamarıa, for share their knowledge with me.

Finally, thank all my friends and people who have been with me in each moment.

vii

Resumen

Se analizaron los principales componentes pictoricos de dos pinturas de caballete llamadas

“San Agustın entre la Sangre de Cristo y la Leche de la Virgen” y “Agustın se presenta

en una vision a Santa Gertrudis”, del siglo XVII para brindar informacion relevante a

curadores y restauradores sobre la paleta de Miguel de Santiago, el pintor ecuatoriano a

quien se atribuyen ambas pinturas. Se recolectaron tres muestras de cada pintura y se

analizaron por espectroscopıa Infraroja y Raman. Asimismo, siguiendo recetas ancestrales

se prepararon dos tintes organicos, laca de carmın a partir de cochinillas secas y molidas

con alumbre; y amarillo de azafran a partir de pistilos secos de las flores de azafran,

para comparar con las muestras. Sin embargo, ninguna muestra evidencio la presencia de

estos pigmentos por los metodos utilizados. El cuadro denominado “San Agustın entre

la Sangre de Cristo y la Leche de la Virgen”, revelo entre sus componentes: pigmentos

ocres (amarillo y rojo), hueso negro, carbonatos asociados al blanco de plomo (albayalde)

y calcita, ligantes proteicos y aceite vegetal. Ademas, esta pintura mostro un compuesto

especial que era el almidon, lo que es un indicio de una probable restauracion a partir

del siglo XVIII, debido a lo reportado en la literatura. Los materiales pictoricos fueron

iguales para el cuadro “Agustın se presenta en una vision a Santa Gertrudis”, un hallazgo

destacable fue la presencia de amarillo plomo-estano tipo I y la posible existencia de

resinas terpenoides.

Palabras clave: FTIR, espectroscopıa Raman, pintura, siglo XVII, Miguel de Santiago.

viii

Abstract

The primary pictorial components of two easel paintings named “San Agustın entre la

Sangre de Cristo y la Leche de la Virgen” and “Agustın se presenta en una vision a Santa

Gertrudis”, from 17thcentury were analyzed to provide relevant information to curators

and restorers about Miguel de Santiago’s palette, the Ecuadorian painter to whom both

paintings are attributed. Three samples from each painting were collected and analyzed

by FTIR and Raman spectroscopy. Also, following ancient recipes were prepared two

organic dyes, the carmine lake from dried and ground cochineal insects with alum; and

yellow saffron from dried pistils of saffron flowers, to compare with the samples. However,

none evidenced the presence of those pigments by the used methods. The painting called

“San Agustın entre la Sangre de Cristo y la Leche de la Virgen”, revealed among its

components: ochre pigments (yellow and red), bone black, carbonates associated with

lead white and calcite, protein binders, and vegetal oil. Moreover, this painting showed

a particular compound, which was starch, being a hint of a probable restoration as from

18thcentury, due to literature reports. The painting materials were the same for the

painting “Agustın se presenta en una vision a Santa Gertrudis”, a remarkable finding was

the presence of lead-tin yellow type I and the possible existence of terpenoid resins.

Keywords: FTIR, Raman spectroscopy, painting, 17thcentury, Miguel de Santiago.

ix

Contents

Autorıa iv

Autorizacion de Publicacion v

Dedication vi

Acknowledgments vii

Resumen viii

Abstract ix

List of Figures xii

List of Tables xiv

List of Abbreviations xv

1 Introduction 1

1.1 Scope of research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.1 Main Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.2 Specific Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Background Information 4

2.1 Painting Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Painting Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2.1 Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2.2 Canvas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2.3 Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2.4 Pigments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.2.5 Fillers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2.6 Binders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2.7 Varnishes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

x

Contents xi

2.3 Degradation of painting compounds . . . . . . . . . . . . . . . . . . . . . . 9

2.4 State-of-The-Art: Analytical techniques for painting materials . . . . . . . 11

3 Experimental Methodology 18

3.1 Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.2 Reference pigments by ancient recipes . . . . . . . . . . . . . . . . . . . . . 18

3.3 Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.4 Characterization Methodology . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.4.1 Infrared spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.4.2 Raman spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4 Results, Interpretation, and Discussion 23

4.1 Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4.2 Spectroscopic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.2.1 Infrared Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.2.2 Raman Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . 44

4.3 Ancient Pigments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

4.3.1 Carmine lake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

4.3.2 Yellow Saffron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

5 Conclusions and Recommendations 48

5.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.2 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

References 50

List of Figures

2.1 Painting structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Polymerization, termination, and degradation reactions taking place by oil

dryness.[25] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.3 Degradation process of linseed oil. (a) An example of a linseed oil molecule,

in green, shows the basic structure of glycerol. Blue branches come from

linoleic acids, and the red ones from linolenic acid. (b) Cross-linking

reaction between linseed oil molecules (black). (c) Formation of carboxylic

acids due to oxidative process.[22] . . . . . . . . . . . . . . . . . . . . . . . 12

3.1 Carmine lake process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.2 Saffron yellow replicated like ancient recipes. . . . . . . . . . . . . . . . . . 20

3.3 Sampling images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.4 Coating process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.5 The blue line corresponds to the equipment’s spectra, and the red one is

the second derivative. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.1 Sampling areas with coated and polished samples taken from paintings

placed at San Agustin Convent. (a) ESA is the code for the flesh-colored

area, R2SA belongs to the red area, and AM1SA corresponds to the yellow

area. (b) 1RSG is the red area code, FASG is for the yellow area, and

ESG is for the flesh-colored area. . . . . . . . . . . . . . . . . . . . . . . . 23

4.2 Infrared Spectrum of the sample FASG . . . . . . . . . . . . . . . . . . . . 25

4.3 Infrared spectrum relation between a) FASG sample and b) Bone black

NIST standard [51] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

4.4 Infrared spectrum of the sample 1RSG. . . . . . . . . . . . . . . . . . . . . 29

4.5 Infrared spectrum of the sample ESG. . . . . . . . . . . . . . . . . . . . . . 32

4.6 Infrared spectrum of the sample AM1SA. . . . . . . . . . . . . . . . . . . . 35

4.7 Infrared spectrum of the sample R2SA. . . . . . . . . . . . . . . . . . . . . 39

4.8 Infrared spectrum of the sample ESA. . . . . . . . . . . . . . . . . . . . . . 42

4.9 Raman spectrum of the sample AM1SA . . . . . . . . . . . . . . . . . . . 44

xii

LIST OF FIGURES xiii

4.10 Infrared standard spectrum. (a) Cochineal, (b) Cochineal with alum, and

(c) Alum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

4.11 Infrared spectra of (a) AM1SA, (b) FASG, and (c) Yellow Saffron standard. 46

List of Tables

2.1 Pigments used around 17th century. . . . . . . . . . . . . . . . . . . . . . . 6

2.2 Some examples of compounds found by Infrared Spectroscopy in artworks

from the 15th century until now. . . . . . . . . . . . . . . . . . . . . . . . . 14

2.3 Some examples of Raman Spectroscopy compounds in artworks from the

15thcentury until now. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.1 Micro-samples detailed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.2 FTIR vibrational bands of the sample FASG. Symbols meaning: w= weak,

vw= very weak, sh= shoulder, s= strong, vs= very strong, ν= stretching,

δ= bending, τ= twisting, as= asymmetric, and s= symmetric. . . . . . . 25

4.3 FTIR vibrational bands of the sample 1RSG. Symbols meaning: w= weak,


δ= bending, τ= twisting, as= asymmetric, and s= symmetric. . . . . . . . 30

4.4 FTIR vibrational bands of the sample ESG. Symbols meaning: w= weak,


δ= bending, τ= twisting, as= asymmetric, and s= symmetric. . . . . . . . 33

4.5 FTIR vibrational bands of the sample AM1SA. Symbols meaning: w=

weak, vw= very weak, sh= shoulder, s= strong, vs= very strong, ν=

stretching, δ= bending, τ= twisting, ρ= rocking, as= asymmetric, and s=

symmetric. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4.6 FTIR vibrational bands of the sample R2SA. Symbols meaning: w= weak,


δ= bending, τ= twisting, ρ= rocking, as= asymmetric, and s= symmetric. 39

4.7 FTIR vibrational bands of the sample ESA. Symbols meaning: w= weak,


δ= bending, τ= twisting, ρ= rocking, as= asymmetric, and s= symmetric. 42

4.8 Summary of results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

xiv

List of Abbreviations

ATR-FTIR Attenuated Total Reflectance-Fourier Transform Infrared

FTIR Fourier Transform Infrared Spectroscopy

GC Gas Chromatography

HPLC-MS High performance liquid chromatography-mass spectrometry

INPC Instituto Nacional del Patrimonio Cultural

IRFC Infrared False Color

IRR Infrared Reflectography

LIBS Laser-Induced Breakdown Spectroscopy

micro-FTIR Fourier Transform Infrared micro-Spectroscopy

MSI Multi-spectral imaging

NIST National Institute of Standards and Technology

OM Optical Microscopy

PLM Polarized light microscopy

SEM-EDX Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy

SERS Surface-Enhanced Raman Scattering

XR X-ray Radiography

XRF X-ray Fluorescence

xv

Chapter 1

Introduction

Nowadays, relevant information worldwide exists about various artworks such as paintings,

ceramic, pottery, textiles, sculptures, and architecture. Their analysis means valuable

data to restorers, museum curators, art historians for dating, authentication, conserva-

tion purposes, or study art history in general [1, 2]. The artworks’ study begins in the

first part of the 18thcentury due to the need to preserve history through art [3]. The art

pieces were seen in danger of loss caused by the effects of environmental conditions over

them. That damage was a motivation to start the analysis of works of art to care for

them. Consequently, the development of conservation chemistry increases in tandem with

the analytical techniques used to accomplish these studies.

This work focuses on the 17thcentury, called the Baroque age. One of the most critical

and development stages of art, even in Ecuador, is the boom of “Escuela Quitena” pieces

of art that recognize many artists. The information provided by the analysis performed

of painting components (dyestuff, binders, resins, varnishes, among others) turns on an

excellent source for restoration and conservation processes. To analyze the components of

a painting is necessary to consider that there are inorganic and organic materials. Then,

there are no specific techniques to analyze them, whereas it is possible to evaluate through-

out a set of techniques that are the most applied since the start of the artwork’s chemical

studies. Those techniques can be destructive, invasive, non-invasive, and non-destructive.

The most useful are non-destructive and non-invasive techniques in patrimonial objects

because the pieces evaluated have great historical importance. The priority is to keep

them as the best as possible.

Despite the several pieces of information about chemical analysis of artworks worldwide,

it is challenging to find it about studying paintings or other Ecuador artwork. It is even

more complicated if the attention is focused on a specific author, as is Miguel de San-

tiago’s case. His complete color palette is not registered. However, according to Pinto

[4] and projects managed by the Department of Investigation from Instituto Nacional del

Patrimonio Cultural (INPC) (Quito, Ecuador), it has a quick revision of the inorganic

materials used. The art information is necessary because Ecuador is a multicultural coun-

1

1.1. Scope of research 2

try and all art pieces are part of its history. Therefore, this work presents the vibrational

spectroscopy study of two paintings from the 17thcentury attributed to Miguel de San-

tiago, an Ecuadorian painter, to contribute valuable information necessary for cultural

heritage.

This work is divided into five chapters. The first one involves the introduction, scope of

research, and the principal and specific objectives. Chapter 2 contains an overview of the

background information about painting materials, degradation, and techniques to analyze

them. The third chapter gives the experimental methodology, including equipment, char-

acterization techniques, and data treatment. Chapter 4 provides results, interpretation,

and discussion. Finally, the conclusions and recommendations are part of Chapter 5.

1.1 Scope of research

This study’s approach involves the contribution of information to future conservation and

restoration processes of artworks due to the deterioration that those and other paintings

suffer. Miguel de Santiago’s pieces were taken as example given that his pieces have

relevant value because most paintings at the San Agustin convent are attributed to this

painter and with the correlation among them, others may be confirmed. Also, the knowl-

edge about his palette also can help to know more about the materials and techniques of

17thcentury.

To achieve the aforementioned is necessary to analyze painting components from two art-

works attributed to this Ecuadorian painter. The way to determine if the compounds

employed belong to the painter’s ones will be by comparing those elements with ones

handled on that stage. On the other hand, compounds that do not correspond to the era

could indicate one or more restorations made through time. With this data, it is possible

to associate the date of restoration with the literature information’s components.

1.2 Objectives

1.2.1 Main Objective

To characterize by vibrational spectroscopy, the primary components present in two easel

paintings named “San Agustın entre la Sangre de Cristo y la Leche de la Virgen” and

1.2. Objectives 3

“Agustın se presenta en una vision a Santa Gertrudis” from the 17thcentury attributed

to Miguel de Santiago.

1.2.2 Specific Objectives

• To make a bibliography review about the analysis of artworks by vibrational spec-

troscopy worldwide and in Ecuador.

• To correlate pigments and materials used in the stage or possibly restorations with

literature examples.

• To replicate carmine lake and yellow saffron by ancient recipes as pigment standards

for sample comparison.

• To provide information about Miguel de Santiago’s palette.

Chapter 2

Background Information

2.1 Painting Structure

Figure 2.1: Painting structure.

Painted artworks are conformed by a multilayer structure with different chemical composi-

tions, as is represented in Figure 2.1. The “support” is the layer responsible for protecting

the work of art from various mechanical impacts. This layer’s possible materials could

be wood, plastic, glass, metal, even rock (frescoes, petroglyphs). The next layer is “can-

vas,” the possible materials for this layer are cotton or linen sized to fit at a stretcher.

Over canvas is applied the “ground,” an intermediate layer between pigments and canvas,

commonly made of gesso, chalk, or lead white pigment. “Paint layers” is the part of the

structure with more relevant information. This stratum contains organic as inorganic

pigments and binders like egg yolk, walnut, linseed, and poppy seed oils. The last layer,

the “varnish,” is transparent, and it could be made of natural or synthetic resins [5, 6].

2.2 Painting Materials

During the 16thand 18thcentury, painting materials were internationalizing. At the end of

the 16thcentury, the trading of colorants and pigments had demanded great production.

Then, the alchemy of that era worked on the developments of that range of production

[7]. In the case of Europe, after the discovery of America, the available painting products

surged on their markets; for example, one of the most used colorants was the carmine from

cochineal. The interchange was more substantial between Europe and America than other

4

2.2. Painting Materials 5

places like Asia or Africa [8]. Considering this antecedent is effortless to determine the

painting elements belong to the 17thcentury worldwide and specifically in Ecuador, at that

moment called Quito. At the end of the 16thcentury, a broad market was developed with

diverse materials imported or local. The offered materials at Quito’s market were, among

others, canvases, wood panels, brushes, oils, rubbers, resins, and pigments. The variety

in that commerce is mostly thanks to the broad and rich environment to provide natural

materials. Besides, successful commerce and art pieces were merits to acknowledging our

ancient painters who were chemical masters in materials and colors [9].

2.2.1 Support

One of the most important things to start creating the artwork is selecting the support

or panel material. It is the base for the rest of the elements that conform to the painting.

The possible materials for this could be wood, glass, metal, or even rock. The standard

panels used during the colonial stage, including the 17thcentury, are made of wood, metal,

or rock [9]. This part of the painting gives stability and security to the painter to perform

the work.

2.2.2 Canvas

The first layer of the whole painting is canvas, and it is a stretcher or a kind of textile used

for easel paintings. Over it is applied all the rest of the layers that form the painting. This

layer’s material can be cotton, linen, paper, leather, glass, metal, and others [5, 6, 10].

During the 17thcentury, the most common materials for easel painting were linen, hemp,

or cotton [8, 9, 10]. It is coating by glues or resins to provide solidity and resistance,

which generally comes from animals and plants. Inside this kind of glues and resins can

be founded rabbit-skin, bone or gluten glue, and dammar, mastic, shellac, or paint tree

resin for the same stage [8, 11, 12].

2.2.3 Ground

In this part of the painting structure, a white color base is applied where the next layer,

which corresponds to pigments, will highlight. This layered material could be made by

gesso, chalk, lime white, led white or zinc oxide pigment over the 17thcentury, according

to the finding from different studies accomplished [13, 14, 15, 16, 11, 17].


2.2.4 Pigments

The pigments layer is where the art is expressed; the combination of colors made possible

an outstanding visualization. The broad palette includes inorganic pigments such as

minerals or metal compounds; and organic colorants from plants or animals. Table 2.1

lists the list of pigments used during the 17thcentury and a description of historical uses

[18, 19].

Table 2.1: Pigments used around 17th century.

Pigments of 17th century

ColorPigment

NameNature Description

Red

Carmine Organic

Used from prehistory until now. Carminic acid

(C22H20O13) extracted from cochineal, insects that

feed on cacti, or Kermesic acid (C16H10O8) from

insects on oak trees. Generally used with alum

solution (Carmine lake).

Madder Organic

Used from the 13th century until now. Obtained

from roots of the madder plant. It contains aliza-

rin (C14H8O4) and purpurin (C14H8O5).

Red lead InorganicUsed from antiquity until the 19th century.

Obtained from mineral minium (Pb3O4).

Red ochre Inorganic

Used from prehistory until the present. It consists

of silica and clay, and its color due to iron oxide

(Fe2O3).

Vermillion/

CinnabarInorganic

Used from antiquity to the 19th century. Obtained

from mineral cinnabar (HgS) crushed and purified

by washing and heating.

Orange Realgar InorganicUsed from antiquity until the 19th century. Close-

related to orpiment, it is arsenic sulfide (As4S4).

Yellow

Saffron Organic

Used around the 16th to 18th century, as pigment

[8] or coating material to conserve others [20].

It comes from Crocus sativus (Saffron) flowers.


Indian

yellowOrg/Inorg

Used around the 15th to 19th century, made from

the urine of cows fed mango leaves. The com-

pound is magnesium euxanthate (C19H16O11Mg

· 5H2O).

Lead-tin

yellow

(Type I)

Inorganic

Used around the 13th to 18th century. The com-

pound is lead-stannate (Pb2SnO4), with a

tetragonal crystal system.

Lead-tin

yellow

(Type II)

Inorganic

Used around the 13th to 18th century. The com-

pound is lead-tin oxide silicate (Pb(Sn, Si)O3), a

cubic pyrochlore crystal system. It was produced

by fusing lead, tin, and quartz at ∼ 800C.

Naples

yellowInorganic

Used from the 16th century until the present,

produced by the calcination of a lead compound

with antimony compound (Pb(SbO3)2 or

Pb(SbO4)2).

Yellow

ochreInorganic

Employed from antiquity until the present. Ob-

tained from silica and clay owing its color to an

iron oxyhydroxide mineral, goethite (FeO(OH)).

Massicot InorganicReported its use around the 17th century. It is

an orthorhombic lead oxide compound (PbO).

Orpiment InorganicUsed from the 13th to 19th century. The com-

pound is arsenic sulfide (As2S3).

Blue

Indigo Organic

Used from the 17th century until present. The

compound is indigotin (C16H10N2O2), from

Indigofera tinctoria L, Isatis tinctoria, and other

similar plant species.

Azurite Inorganic

It is an artificial blue, from the 17th until now.

Produced by azurite mineral (Cu3(CO3)2(OH)2)

ground, washed, and sieved.


Smalt Inorganic

The pigment was used between the 15thto 18th

centuries. The compound is a potassium glass

containing cobalt.

Ultramarine Inorganic

Used from 12th until present. It is a complex

sulfur-containing sodium aluminum silicate by

the ground of lapis lazuli by mixing it with wax

and kneading in a dilute lye bath.

White

Lime

white,

Chalk

InorganicUsed from prehistory until now. Obtained from

limestone mineral or calcite (CaCO3).

Gypsum InorganicUsed around the 17th century for the ground

layer, and the compound is CaSO4·2H2O.

Lead

whiteInorganic

Used from the 13th to 19th century. The com-

pound is 2PbCO3·Pb(OH)2, and it is obtained

from hydrocerussite.

Green

Copper

resinateInorganic

Used around the 15th to 17th century. Produced

by turpentine, some waxes and pieces of verdi-

gris boiled together.

Green

earthInorganic

Its use was from antiquity to the present. It is

a complex aluminosilicate mineral.

Malachite Inorganic

Used from antiquity to possibly the 18th century

[21]. It is a natural mineral (2CuCO3.Cu(OH)2)

ground to powder.

Verdigris Inorganic

Employed around middle age and 19th century.

The covering of copper plates prepares

Cu(OH)2·(CH3COO)2·5H2O with acetic acid.

Brown Umber Inorganic

Used from prehistory until the present. It is a

mixture of minerals, essentially rust-stained clay

(Fe2O3(·H2O) + MnO2·(nH2O) + Al2O3).

Black

Charcoal,

Carbon

black

Inorganic Used from prehistory until now.

2.3. Degradation of painting compounds 9

Bone

blackInorganic

It is used from prehistory until now. Obtained

by charring bones (osseous parts of animals) or

waste ivory.

2.2.5 Fillers

They are generally used in textiles to fix the colorants of the different kinds of fibers.

However, in paintings used to help the pigments fix on canvas, commonly, those are

mixed with colorants, and it is also called mordant. In the 17thcentury, the most frequent

filler or mordant for the carmine lake was the alum, a hydrated double sulfate salt of

aluminum [9].

2.2.6 Binders

Binders are essential for the use of colorants, and those made the pigments consistent

to allow the painter to portray its art. The binders used around the 17thcentury include

mainly oils (walnut, olive, linseed, turpentine), protein (egg yolk, casein), even resins such

dammar, shellac, mastic, and others [8, 11].

2.2.7 Varnishes

Varnish is the last layer, it is transparent, giving to the painting an effect of glazing.

Occasionally, this structure is absent. The main materials in this structure are resins,

which could be natural (shellac, amber, dammar) from insects, tree resins or fossils; and

synthetics (Polymers), which ones appear in the last century [22].

2.3 Degradation of painting compounds

The chemical degradation of painting compounds is unavoidable. The time and envi-

ronmental events leave the mark of their passage. Exist many factors that can affect

the paint’s composition and appearance, including exposure to light, humidity, oxygen,

different temperature, air pollutants, and pests and microorganisms such as fungi and

bacteria [5, 23]. According to Gavrilov, Maev, and Almond [5], the most common types

of deterioration involve:

• Darkening and change of color: Illumination, humidity, and pollution induce chem-

2.3. Degradation of painting compounds 10

ical reactions in paint layers resulting in a color change.

• Craquelure and wear of materials: It means the appearance of cracks due to different

reasons like a considerable impact, weakening of the ground, and stiffness of paint.

• Cleavage and layer detachment: It affects more between the ground and the support

layers. It is caused by the age of materials and the change of stiffness.

• Insects or animal damage: The presence of organic components results in a food

source for rodents or insects and their larvae. Linen or wool canvases are the most

affected by rodents.

• Bio-deterioration: The damage caused by fungi and bacteria affects the paint binders

and canvases, making rotting.

The complexity and diversity of painting materials added to the aging process’s chemical

changes denote a significant challenge to identify the original elements in cultural heritage

creations. However, there are products of degradation that make possible to infer or

define painting component even the aging effect. It is the case of binders made of lipids or

proteins, and those suffer the consequence of time by oxidation. This oxidation triggers

polymerization of triglycerides and phospholipids, cross-linking, and the formation of low

molecular weight carbonyls, volatiles, unsaturated compounds, oxidation of cholesterol,

and also free radicals [24]. Figure 2.2 shows the reactions taking place by oil dryness [25],

and Figure 2.3 is an example of a linseed oil aged process [22].

Some Italian paintings analyzed by Infrared and Raman spectroscopy show carbonyl sub-

products by dry oils, such as the broad infrared band around 1730 cm−1where the sharp

band of fresh oils [26]. On the other hand, age in pigments is also present because of

the reactions between pigments and binders, which means interactions among metals,

lipids, and proteins. Metal ions such as copper, cobalt, lead, manganese, and iron can

act as polymerization catalysts opposing vermillion (HgS) and black carbon, which retard

this polymerization process [24]. Some metal ions, due to the polymerization, react with

fatty acids resulting in metal carboxylates. Numerous studies of aged painting materials

appear this product as degradation of organic materials [17, 27]. Other elements that

suffer the effect of time are resins, such as mastic or dammar, generally in the 17thcentury

[11, 28]. These resins are mainly composed of terpenoids that oxidize quickly, causing

cracking, yellowing, and color fading [24]. One of the most common pigments, lead white,

considered the primary white rendering pigment [29], has as degradation products lead

2.4. State-of-The-Art: Analytical techniques for painting materials 11

Figure 2.2: Polymerization, termination, and degradation reactions taking place by oildryness.[25]

carboxylates and carbonates. Those products help identify and verify the original artist’s

palette [30], in concordance to Annelies [31], who studies hydroxyapatite deterioration in

17thoil paintings. The damage involves the whitening of bone black (hydroxyapatite) and

also the cracking of some paintings. With these antecedents, it is possible to tell that even

the lack of original pictorial components exists marks that can help to match residues of

different chemical reactions that occur through the initial ones.

2.4 State-of-The-Art: Analytical techniques for paint-

ing materials

The painting composition has a high level of complexity, and it is the reason to apply

multiple techniques to identify each element present. To select the appropriate techniques

for analyzing historical objects is essential to consider which of them do not represent art-

work’s damage. This consideration is the most important because of the prized value of art

pieces, whose looking for non-invasive and non-destructive methods. Nonetheless, not all

analytical techniques comply with that considerations, and it makes it possible to classify

the most favorable methods to apply in cultural heritage studies. There are a lot of analyt-

ical techniques such as spectroscopy, chromatography, microscopy, and imaging methods.


(a) (b)

(c)

Figure 2.3: Degradation process of linseed oil. (a) An example of a linseed oil molecule,in green, shows the basic structure of glycerol. Blue branches come from linoleic acids,

and the red ones from linolenic acid. (b) Cross-linking reaction between linseed oilmolecules (black). (c) Formation of carboxylic acids due to oxidative process.[22]

All of them provide relevant data for the elucidation of components inside a graphical

object; however, some of those techniques result in being invasive and destructive for

artworks. Non-invasive methods play a primary role in studying artwork [14], generally

are imaging techniques and those not need to detach samples from the whole painting.

Among them are high-resolution digital photography in visible light, UV Reflectance and

Fluorescence, X-ray Radiography (XR), Infrared Reflectography (IRR), Infrared False

Color (IRFC), Multi-spectral imaging (MSI) [19], Trans-illumination, Trans-irradiation

techniques, and others [14]. Although, composition and structural aspects from strati-

graphic information are not possible to detect just with non-invasive techniques.

Consequently, more analytical techniques are required; here appears chromatography,


microscopic, and spectroscopic ones as complementary methods. For example, in two

paintings, “Servilius Appius” by Isaac van den Blocke and “Allegory of Wealth” prob-

ably by Anton Moller from the 17thcentury, were found the presence of organic binders

such as oils and protein by Fourier Transform Infrared Spectroscopy (FTIR). These kinds

of binders and ground layers were confirmed by Gas Chromatography (GC) as linseed

oil and casein [28]. A similar case is reported in a Belarusian painting, where combine

techniques like Laser-Induced Breakdown Spectroscopy (LIBS), Surface-Enhanced Raman

Scattering (SERS), Fourier Transform Infrared micro-Spectroscopy (micro-FTIR), Opti-

cal Microscopy (OM), XR, and Luminescence [11]. Also, it could include other techniques

such as Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDX)

and X-ray Fluorescence (XRF) as in the research of pigments and materials used by the

famous Romanian painter Nicolae Grigorescu in his three artworks [29]. Infrared and Ra-

man spectroscopy are the most common techniques considered non-destructive; those are

invasive because it is necessary samples taken from paintings. However, there is the pos-

sibility of turning those into non-invasive and non-destructive using portable equipment

[13].

In this work will be applied Infrared and Raman spectroscopy as invasive and non-

destructive techniques. With these methods, it will be possible to identify binders, organic

and inorganic pigments, and coatings. Nevertheless, the accuracy will be limited, for in-

stance, to prove the existence of oil and not that if it belongs to nuts, olive, or another

source. To complete the data will be necessary complementary techniques and historical

information about the components used in the same age of the analyzed paintings and be

associated with the materials found.

Infrared Spectroscopy. This method is based on the vibration of atoms of a molecule

subjected to infrared radiation. The interaction between matter and light incidence can

be interpreted as changes in dipole moments of a molecule related to vibrations and

rotations. The mathematical method of Fourier transformation in infrared spectroscopy

takes the idea of radiation interference to produce an interferogram [32]. FTIR spectra can

be obtained by different techniques, like Attenuated Total Reflectance-Fourier Transform

Infrared (ATR-FTIR). It is a form of internal reflection spectroscopy with an internal

reflection element, a diamond crystal, with a high refractive index [33].


This method’s use implies the detection of organic components and characteristics of

some elements that have been suffered deterioration. Some studies were carried out by

infrared spectroscopy to identify binding media, such as proteins, triglycerides, fatty acids

or resin acids, and metal soaps as degradation products. The compounds finding in diverse

artworks by this technique are detailed in Table 2.2.

Table 2.2: Some examples of compounds found by Infrared Spectroscopy in artworksfrom the 15th century until now.

Artwork/Painter Compounds Ref.

Modern PaintingsAcrylic and alkyl binder and artificial Ultra-

marine blue.[34]

“Old Lady with basket”

“The young Shepherd”

“The return from fair”

by Nicolae Grigorescu

Fatty acids, metal soaps, esters,

triglycerides, metal carboxylates, amides

(proteins), carbonates, ultramarine/lazurite,

silicates, gypsum, red ochre.

[29]

Piero Galardi Synthetic materials, polyurethane. [35]

Manuscripts Illuminations

by Manizola

Red lake, read lead, vermillion, carbonates

, proteins (Amides), lead white, silicates.[36]

“The coronation and

assumption of the Blessed

Virgin Mary” in Poland

Chalk, lead white, ivory black, smalt/

azurite/ultramarine, proteins, triglycerides/

fatty acids, silicates, carbonates, carboxylates,

red ochre.

[16]

“Virgin Eleusa” in

Belarussia

Oils, zinc white, proteins (Amides), chalk,

dammar/mastic resins.[11]

“The king watering lemons”

“Hunting scenes”

Esters/Triglycerides, carbonates, carboxylates,

proteins (Animal glues), arabic gum, silicates,

ultramarine.

[17]

“Servilius Appius” by Isaac

van der Blocke, “Allegory of

Wealth” by Anton Moller

Oils, proteins (casein), carbonates, gluten glue. [28]

General Studies Esters/Fatty acids [37]


Infrared Spectroscopy

in Conservation

Oils, ultramarine, proteins, triglycerides/

Fatty acids, silicates, carbonates, carboxylates,

resins, blood.

[38]

“A woman weighing Gold”

by Jan Vermeer

Indian yellow: Glucuronic acid salt,

Euxanthane.[39]

Jose BenlliureDry oils, lead white, esters/triglycerides,

carboxilates.[3]

“Virgin and Child” Varnishes and binders [40]

“The landscape with a

ploughman” (Private

Property)

Barium sulfate, triglycerides, carboxylates,

carbonates, dry oils, free fatty acids, lead

white, Prussian blue, proteins, silicates.

[27]

Von ImhoffFatty acid, esters, carbonates, carboxylates,

silicates.[25]

Raman Spectroscopy. This spectroscopic method is based on Raman scattering, where

photons lose or gain energy through interactions with sample’s vibrating molecules [41].

The scattering light employs knowledge about molecular vibrations, providing information

regarding the structure, symmetry, electronic environment, and bonding of the molecule

[42]. Sometimes, a troublesome source of noise in Raman spectroscopy is fluorescence

emission, which can hide or mask the spectrum. This effect is produced generally by

organic samples [41].

Raman spectroscopy studies mostly inorganic components in cultural heritage objects. In

this case, it is used for organic and inorganic painting elements. However, the quality of

results depends on the lasers used, the sample’s complexity, and the presence of fluores-

cence produced by organic components. Inorganic compounds’ analysis is affected because

numerous organic dyes’ fluorescence is intensely even at 785 nm excitation. It results in

the obscuring of background in the spectrum, making Raman identification, in some cases,

impossible [43, 44]. Some organic components can be analyzed with Raman, for example,

natural fibers, resins, and binding media (proteins, fatty acids, polysaccharides) [44]. In-

organic pigments are the most common compound analyzed by this technique. Table 2.3

details some examples of compounds founded in artworks from the 15thcentury until the


present.

Table 2.3: Some examples of Raman Spectroscopy compounds in artworks from the15thcentury until now.

Artwork/Painter Compounds Ref.

Modern Paintings Chromium oxide, cadmium yellow. [34]

“Old Lady with basket”

“The young Shepherd”

“The return from fair”

by Nicolae Grigorescu

Carbon black, vermillion, hydrocerussite,

lepidocrocite, chrome yellow.[29]

The Church of S. Maria as

undos in Idro./Italy

Hematite, azurite, cerussite, green earth,

calcite, goethite, malachite, plattnerite.[14]

Manuscripts Illuminations

by Manizola

Chalk, azurite, lead white, kaolinite, proteins

(Amides).[36]

Italian Paintings by

Giovanni Battista Langetti

and Luca Giordano

Massicot, litharge, lead-tin yellow type I,

lead-tin yellow type II, lead antimonate.[45]

“The coronation and

assumption of the Blessed

Virgin Mary” in Poland

Cinnabar [16]

“Virgin Eleusa” in

BelarussiaCerulean [11]

European and South

American works of artCalomel [46]

“Lot and his daughters” by

G.B. Langetti, “Entrance

of Christ in Jerusalem”

by Luca Giordano

Lead-tin yellow type I, tetragonal lead

oxide (Litharge), lead-tin yellow type II,

naples yellow, massicot.

[47]

“Servilius Appius” by

Isaac van der Blocke

“Allegory of Wealth” by

Anton Moller

Lead-tin yellow type I, chalk, lead white,

Cinnabar.[28]


“Carahuara de Carangas”

“Sacristıa de Santiago de

Callapa”, “San Jose de

Sorachi”, “Copacabana

de Andamarca”

Cinnabar, carbon, copper phthalocyanine,

benzimidazolone, indigo, antlerite, hematite,

gypsum, goethite, β − naphtol, rutile.

[48]

Jose Benlliure Dry oils, polysaccharides, proteins, resins. [3]

“Virgin and Child”Red lead, massicot, lead white, chalk,

bone white.[40]

Medieval artworks

Proteins (albumin, casein, fish glue, gelatin,

isinglass); Polysaccharides (rabic and cherry

gum, starch, tragacanth); Fatty acids (beewax,

linseed, poppy-seed, walnut, sunflower oils);

Resins (shellac, dammar, colophony, sandarac,

elemi, Kongo copal); Lead-tin yellow type I.

[44]

Chapter 3

Experimental Methodology

3.1 Equipment

In the case of standards were used a GLASSCO Heating mantle with 150 power watts,

a Hot plate stirring MS300HS M TOPS, a BUCHI R–210 Rotavapor and a Drying oven

SLN 115 POL-EKO-APARATURA.

The samples’ treatment was achieved with an Olympus SZH Stereo Microscope, a Struers

DP-U2 Mineralogical Polish, and an Olympus BX53 Microscope.

In the characterization of samples were used a JASCO FT/IR-4200 type A with a PRO450-

S Zn-Se attenuated total reflection (ATR) crystal, and a Triglycine sulfate (TGS) detector;

and a LabRam HR Evolution Raman spectrometer from Horiba Scientific (Jobin Yvon

Technology), equipped with a 633 and 532 nm laser sources working on 180 degrees’

reflection using a Syncerity CCD.

3.2 Reference pigments by ancient recipes

Carmine lake and yellow saffron were prepared from ancient recipes or treatises to create

pigment standards and analyze if they are part of the studied artworks. The presence of

these pigments is suspected due to those are organic dyes used around the 17thcentury.

Carmine lake standard. This process was based on ancient recipes from a document

about treatises by Pacheco and Palomino [49] and Douma’s information. The Figure

3.1 ilustrates the process where first, cochineal was collected from prickly pear cactus

and dried in the oven at 40C for 12 hours. After that, dried cochineal was sifted to

remove impurities as much as possible. The dried and cleaned cochineal were crushed in

a porcelain mortar. Then one part was solved in water with alum (carmine lake standard)

and the other without alum (blank). Finally, both aqueous phases were filtered and dried.

The ATR-FTIR spectra were taken from the dried solids obtained, carmine lake standard

and blank; also, a spectrum from alum alone.

18

3.3. Sampling 19

Figure 3.1: Carmine lake process.

Yellow saffron standard. This process showed in Figure 3.2, starts from the document

based on Pacheco and Palomino’s treatises [49], which showed the need for dried pistils

from saffron flowers. Those were bought. Then, pistils were boiled in water with ashes

for around 10 to 20 minutes. It was filtered, and the liquid was stored with ethanol in

the freezer. The yellow liquid was dried to take the ATR-FTIR spectrum.

3.3 Sampling

The sampling process, in Figure 3.3, guided by INPC staff was carried out for two paint-

ings, “San Agustın entre la Sangre de Cristo y la Leche de la Virgen” and “Agustın se

presenta en una vision a Santa Gertrudis,” both attributed to Miguel de Santiago. A

scalpel tip was pressed inside the desired area to obtain micro-samples and brought it out

with carefulness. To the FTIR analysis was not necessary any treatment for the samples.

After that, to preserve samples, those were encapsulated inside acrylic. This treatment,

showed in Figure 3.4, starts with an acrylic matrix where was placed until the middle

of each cubicle, white acrylic powder with methacrylate drops covering it. After acrylic

polymerization, the sample was placed into the middle of this polymerized acrylic cube.

3.3. Sampling 20

Figure 3.2: Saffron yellow replicated like ancient recipes.

It was achieved carefully and helped by a stereoscope and thin tweezers or needles to

manipulate the samples due to their reduced size. Then, the entire cubicle was filled with

white powder acrylic and drops of methacrylate with much caution. Once solidified, they

were polished until observing the sample in the coating surface.

Figure 3.3: Sampling images

3.4. Characterization Methodology 21

Figure 3.4: Coating process.

3.4 Characterization Methodology

3.4.1 Infrared spectroscopy

For the acquisition of the spectra, pristine samples were used without any previous treat-

ment. Each sample measured by JASCO is placed into the crystal and analyzed in a

spectral range from 4000 cm−1to 550 cm−1. The scan number was 50, and the spectral

resolution was 4 cm−1.

To the treatment of infrared data was used OMNIC9, a software from Thermo Fisher Sci-

entific Inc. In this program, the second derivative, Fourier self-deconvolution, and fitting

curve because of the samples’ complexity and the overlap of signals were applied. Those

settings aim to identify the principal signals hidden or overlapped by others and obtain

a better result. In Figure 3.5 at 1727 cm−1is possible to appreciate in the blue line a

signal with soft shoulders, meaning probably overlapped bands that are unmask using the

second derivative.

3.4. Characterization Methodology 22

Figure 3.5: The blue line corresponds to the equipment’s spectra, and the red one is thesecond derivative.

3.4.2 Raman spectroscopy

The Raman spectra of samples were taken in a LabRam HR Evolution Raman spectrom-

eter with a grating of 800 lines and the 3.2% of laser power from 2 mW on 633 nm and 5

mW on 532 nm at 100%; it means 64 µW in 633 nm and 160 µW for 532 nm.

This work obtained a unique spectrum from the sample AM1SA, which was compared

with an IBeA Database [50] spectrum to analyze the components present.

Chapter 4

Results, Interpretation, and Discus-

sion

4.1 Samples

This work analyzed two paintings from the 17thcentury, “San Agustın entre la Sangre de

Cristo y la Leche de la Virgen” and “Agustın se presenta en una vision a Santa Gertrudis,”

both attributed to the Ecuadorian pinter, Miguel de Santiago. Due to the high historical

value of these art pieces, the extract of samples was limited, and it was possible to obtain

three micro-samples from each painting and different zones. Figure 4.1 shows the coated

and polished samples and the place from which they are.

(a) “San Agustın entre la Sangre de Cristo y laLeche de la Virgen”

(b) “Agustın se presenta en una vision a SantaGertrudis”

Figure 4.1: Sampling areas with coated and polished samples taken from paintingsplaced at San Agustin Convent. (a) ESA is the code for the flesh-colored area, R2SAbelongs to the red area, and AM1SA corresponds to the yellow area. (b) 1RSG is the

red area code, FASG is for the yellow area, and ESG is for the flesh-colored area.

23

4.2. Spectroscopic Analysis 24

Table 4.1: Micro-samples detailed

Painting Sample Code Description

San Agustın entre la Sangre deCristo y la Leche de la Virgen

ESA Flesh-colored areaAM1SA Yellow areaR2SA Red area

Agustın se presenta enuna vision a Santa Gertrudis

ESG Flesh-colored areaFASG Yellow area1RSG Red area

4.2 Spectroscopic Analysis

Most of the results come from the spectra taken by the ATR-FTIR spectrophotometer,

all samples were analyzed, and each one provided information about Miguel de Santiago’s

palette. In contrast, Raman spectroscopy was able to obtain only one result from the

AM1SA sample. The analysis of every sample is related to literature data to deduce the

materials employed in each artwork or correspond to another stage different to 17thcentury.

There are some unidentified bands in the spectrum data tables, which probably correspond

to metal oxides not defined in this work due to the limitations of the samples’ size and

treatment limitations.

4.2.1 Infrared Spectroscopy

“Agustın se presenta en una vision a Santa Gertrudis”

The FTIR spectrum in Figure 4.2, belong to the cross-section, FASG, has dominant bands

that show distinct phosphate group at 1091(vs) cm−1and 1046(vs) cm−1(νPO3−4 ), those

correspond to calcium phosphate Ca3(PO4)2, which is the main component of Bone black

[38, 31, 51]. There are other complementary bands of phosphates with less intensity at

960(sh), 873(w), and 800(m) cm−1. In Figure 4.3, as a reference is observed the spectrum

of the FASG sample (a) and below, as a standard from the National Institute of Standards

and Technology (NIST), Bone black spectrum (b), showing the coincidence of top bands.

This black pigment, which is reported in 17thcentury [31], is formed mostly of Ca3(PO4)2

and less C and CaCO3.


Figure 4.2: Infrared Spectrum of the sample FASG

Table 4.2: FTIR vibrational bands of the sample FASG. Symbols meaning: w= weak,vw= very weak, sh= shoulder, s= strong, vs= very strong, ν= stretching, δ= bending,

τ= twisting, as= asymmetric, and s= symmetric.

Wavenumber

(cm−1)Intensity Vibration type Assign

∼3300 wνO-H Hydroxyl group

νN-H Amide [52]

2958 w

νC-H (sp3) Hydrocarbon chains [17, 28, 26]2924 w

2854 vw

1745 shνC=O

Fatty acids and triglycerides

1726 w esters [17, 27]

1712 sh νC=O Carboxylic acids [16, 27]

1664 w νC=O Amide I [52]

1642 wνC=O Amide I [52]


νasCOO− Calcium oxalate [17]

1570 vw νasCOO−Metal oxalates, soaps, and car-

boxylates [16, 17, 27, 53]

1547 vw

δN-H, νC-N Amide II [52, 27]

νCOO−

Metal soaps and carboxylates

[16, 27, 53]

1469 w δCH2, δasCH3 Aliphatic chains [38, 25]

1449 w δCH2, δsCH3

Aliphatics chains [28]


[16, 53]

1428 vw δCH2


[16, 53]

1391 w

δsCH3

Fatty acids and triglycerides [38,

25]

νas(CO2−3 )

Carbonates or metal carbonates

[27, 53]

1319 w

νsCOO− Oxalates [16, 54]

νsC-OCarbonates or metal carbonates

[27, 53]

1261 w νC-O Triglyceride ester linkage [26]

1091 vs νPO3−4 Phosphates - Bone black [38]

1046 vs

νPO4 Phosphates - Bone black [38]

νsC-OCarbonates or metal carbonates

[16, 26, 27, 53]

1021 sh νSi-O-Si Silicates [27]

960 sh νPO3−4 Phosphates - Bone black [38]

935 w νAl-O-H Alumino-silicates [27]

873 w νPO3−4 Phosphates - Bone black [38]

830 sh δCOO−Carbonates or metal carbonates

[16, 26, 27, 53]

800 mνP-OH Phosphates - Bone black [38]


νSi-O Silicates [16]

743 m τCH2; C-(CH2)n-C,Aliphatic chains [38]

712 m n>4

693 m νSi-O Silicates [16]

675 sh δCOO−


[16, 27]


[16, 26, 27, 53]

614 m Unidentified

598 m Unidentified

569 m Unidentified

Furthermore, in Figure 4.2 and Table 4.2 other signals with less intensity are present,

such as N-H stretching from amides, overlapped with νO-H at ∼3300 cm−1from other

compounds. The bands at 2958, 2924, and 2854 cm−1correspond to νC-H (sp3) of the hy-

drocarbon chains (fatty acids and proteins) [17, 28, 26]. Also, bending of C-H bonds from

aliphatic chains of fatty acids and triglycerides appear at 1467 cm−1and 1391 cm−1(δsCH3)

[38, 25], and C-H torsion at 743(m) and 712(m) cm−1[38]. The C=O stretching vibrations

of carbonyls associated with fatty acids, triglycerides [16, 27] and from the additional

formation of ketones, esters, and carboxylic acids as a result of the hydrolysis of glyc-

erol esters during oxidative polymerization by degradation process appears at 1745(sh),

1726(w), and 1712(sh) cm−1[26, 25]. The second derivative of the spectrum presents the

shoulders bands. Carbonyl bands suggest lipidic binders [27], which could be vegetal oils,

like linseed, olive, walnut, and lavender oil, commonly used in the 17thcentury according

to a Danish apothecary [8]. Nonetheless, the most probably could be linseed oil due to

the international commerce in that stage [8, 28, 31]. Additionally, there is a band at 1261

cm−1for νC-O due to triglyceride ester linkage important for the oxidative polymerization

as was showed in Figure 2.2 [26].

The presence of proteins is evidenced by the most prominent vibrational bands of the

protein backbone. Those are the νC=O at 1664 and 1642 cm−1of amide I, and δN-H

(40-60% of the potential energy), νC-N (18-40%) around 1547 cm−1of amide II [52] from

the proteins secondary structure [27, 55, 56, 57]. Based on previous signals is possible


to associate protein binders to egg, casein, or animal glue (fish glue or rabbitskin glue)

[58] founded in some analyzed paintings from 17thcentury [17, 28]. The derivatives from

the decomposition of organic materials could be metal oxalates, soaps, or carboxylates

and their signals appear at 1605(sh) cm−1(νasCOO−), 1570 cm−1(νasCOO−) cm−1, 1319

cm−1(νsCOO−), 675 (δCOO−) cm−1, 1449 cm−1(δCH2, δsCH3), and 1428 cm−1(δCH2)

[17, 26, 27, 53].

Besides, lead-white (2PbCO3Pb(OH)2) is an expected white pigment generally used for

ground layer, or white zones handle around the 13thto 19thcentury. It was discovered in

many paintings studied worldwide [59, 13, 16, 60, 11, 1], even in Peru, being a referent for

Ecuadorian paintings due to the closeness with the country [21]. The bands attributed to

this white pigment because of its content of carbonates or metal carbonates are observed

at 1547 cm−1(νCOO−), 1391 cm−1(νas(CO2−3 )), 1319 cm−1(νC-O), 1046 cm−1(νsC-O), 830

cm−1, and 675 cm−1[16, 27, 25, 61]. Silicates and alumino-silicates were found, and those

possibly mean the existence of kaolinite as a lead-white impurity at 1021 cm−1(νSi-O-Si),

935 cm−1(νAl-O-H), 800 cm−1(νSi-O), and 693 cm−1(νSi-O) [27]. Also, it is possible the

presence of them as impurities by the existence of yellow ochre. It could be taking into

account the previous information recovery by INPC that reported the use of iron oxides

[62].

Figure 4.3: Infrared spectrum relation between a) FASG sample and b) Bone blackNIST standard [51]


In the spectrum of the sample 1RSG in Figure 4.4 and Table 4.3, the main band could

contain a huge amount of signals overlapped. The band around 1015 cm−1could be at-

tributed to the C-O-H interaction from sugars of cellulose belong to canvas which could

be linen or cotton [38]. A piece of the canvas may have been taken at the moment of

sampling. However, this band could appertain to starch, its use is reported as an additive

to obtain different tones of carmine [49] and during 18thcentury is reported the use of

cochineal with cinnabar and starch as a binder [63], it is able to match this found with a

possible restoration in that stage.

The broadband between 1200 and 900 cm−1may include signals of silicates and alumino-

silicates, maybe from kaolinite as red ochre’s impurity [29], by the bands at 1076 cm−1(νSi-

O), 1024 cm−1(νSi-O-Si), 1006 cm−1(νSi-O-Al), 935 cm−1(νAl-OH), and 904 cm−1(νAl-

OH) [27]. Hematite (Fe2O3), a red pigment from the 17thcentury [64, 25], its presence was

demonstrated by an analysis achieved in 2014 by INPC [62], where it shows the content

of iron oxides in the painting.

Figure 4.4: Infrared spectrum of the sample 1RSG.


Table 4.3: FTIR vibrational bands of the sample 1RSG. Symbols meaning: w= weak,vw= very weak, sh= shoulder, s= strong, vs= very strong, ν= stretching, δ= bending,


Wavenumber



νN-H Amide [52]

2923 wνC-H (sp3) Hydrocarbon chains [17, 28, 26]

2856 w

1743 vw νC=O Esters [17]

1710 w νC=O Carboxylic acids [16, 27]

1686 sh νC=O Amide I [52]


νasCOO− Oxalates [17]

1607 sh νC=C Aromatic [28]

1567 w δN-H, νC-N Amide II [52]

1534 w δN-H Amide II [52]

1506 shνC=C Aromatic [28]

δN-H Amide II [52]

1466 w δC-H Aliphatic chains [38, 25]

1454 wC-H deformation

Oils and proteins [28]in –CH2- and –CH3

1424 w νC-O Carboxylates [26]

1393 w νC-O Carbonates [27]

1371 sh δC-H Aliphatic chains [38, 25]

1320 w νsCOO− Oxalates [17]

1102 m νC-O Triglycerides

1076 sh νSi-O Silicates [16]

1024 s νSi-O-Si Silicates [27]

1015 s νC-O-H Starch [63]

1006 sh νSi-O-Al Alumino-silicates [27]

935 mνAl-OH Alumino-silicates [27]


904 sh

868 sh νC-O Calcite [17, 38, 27]

789 m Unidentified

723 mτC-H Aliphatic chains [38]

701 m

680 m δCOO− Carbonate – Lead white [17, 26]

The O-H vibrations overlap the signals for N-H stretching of amides at ∼3300 cm−1. The

other vibration bands at 2923 and 2856 cm−1come from symmetric and asymmetric C-H

stretches of hydrocarbon chains fatty acids and proteins [28]; the low intensity of them is

caused by the loss of some hydrocarbons [26]. Also, C-H bending from the chains of fatty

acids are observed at 1466 and 1371 cm−1[38, 25] by the application of the second deriva-

tive, the C-H deformation is showed at 1454 cm−1, and C-H torsion from aliphatic chains

possibly by vegetal oils at 723 and 701 cm−1[38]. The signals belong to C=O stretching

are 1743 and 1710 cm−1, and the last one, with the bands at 1424 cm−1(νC-O), suggests

the formation of carboxylates [26].

The band’s widening around 1730 cm−1could be due to different ketone, ester, and acid

carbonyl formation as degradation products of the aging of vegetal oils from binders [11,

26, 25]. Around 1102 cm−1appear C-O stretches from triglycerides of oils. The existence

of amides evidence protein binders such as egg, casein, or animal glue [11, 17, 28, 58],

with C=O vibrations at 1686 and 1640 cm−1of amide I; and N-H bending and C-N stretch

at 1567, 1534, and 1506 cm−1of amide II, the most representative bands for proteins sec-

ondary structure [52, 55, 56, 57]. Additionally, the C=C interaction from aromatic amino

acid ring modes are present at 1607 and 1506 cm−1making a few contribution to the in-

tensity of protein amide bands [52, 28].

Oxalates, the degradation products of organic materials, are present at 1640 cm−1(νasCOO−)

and 1320 cm−1(νsCOO−) [17]. The vibrational bands at 1393 cm−1(νC-O) may indicate

metal carbonates [16, 17, 27]. The absorbance at 868 cm−1suggests the existence of calcite

(CaCO3) [38, 27], which is possible because it is an impurity of the use of red ochre [29],

without ruling out the possibility of lead carbonate because of the band at 680 cm−1which

is considered evidence of it [17, 26].


In the sample ESG, the spectrum in Figure 4.5 and Table 4.4, the prominent bands at

1096, 1029, 870, 605, and 577 cm−1(νPO3−4 ) are associated with the presence of calcium

phosphate Ca3(PO4)2 from Bone black, a typical pigment around 17thcentury [38, 31].

The bands at 697 cm−1(νSi-O), 795 cm−1(νSi-O), and 915 cm−1(νAl-OH) correspond

to quartz and kaolinite (silicates and alumino-silicates) [27]. Quartz and kaolinite are

generally considered impurities of ochre pigments (Goethite, hematite, or both) [29, 54].

The symmetric and asymmetric C-H stretching of hydrocarbon chains from free fatty

acids and proteins are shown at 2956, 2927 and 2861 cm−1[28] with a low intensity, which

is the product of the loss of some hydrocarbons [26]; C-H bending from aliphatic chains

are shown at 1458 cm−1, and for C-H torsion at 743, 721 cm−1. A band related to the

aged of oil is observed at 1797 cm−1, attributed to reactive peracid and perester products

[26]. The bands at 1747 and 1713 cm−1are for the presence of C=O stretching of ester,

ketones, and acid carbonyls as sub-products formed by oxidative polymerization [17, 26,

25]. The probable oils, taking into account the literature information about vegetal oils

used around the 17thcentury, candidates could be linseed, olive, walnut, and lavender oil,

being linseed oil the most popular in that stage [8, 28, 31].

Figure 4.5: Infrared spectrum of the sample ESG.


Table 4.4: FTIR vibrational bands of the sample ESG. Symbols meaning: w= weak,vw= very weak, sh= shoulder, s= strong, vs= very strong, ν= stretching, δ= bending,


Wavenumber


2956 w

νC-H Hydrocarbon chains [17, 28, 26]2927 w

2861 vw

1797 vw νC=OPeracid and perester products

[26]

1747 w νC=O Triglyceride esters [17, 27]

1713 w νC=O Carboxylic acids [16, 27]


1665 w


νasCOO− Oxalates [16, 17, 27]

1547 wδN-H, νC-N Amide II [52, 65]

1522 w

1510 wδN-H Amide II [52]

νC=C Aromatics [28]

1458 wC-H deformation


1396 w νC-O Metal carbonates [27]

1262 w νC-O Triglyceride ester linkage [17, 26]

1096 m νN-C-O Triglycerides [17]

1029 sνPO3−

4 Bone black [38]

νSi-O-Si Silicates [27]

∼910 w νAl-OH Alumino-silicates

∼870 w νPO3−4 Phosphate - Bone black [38]


743 mτC-H Vegetal oil [38]

721 m



680 m δCOO− Carbonates [16, 17, 26]

605 S νPO3−4 Phosphate - Bone black [38]

Additionally, around 1262 cm−1can identify triglyceride ester linkages produced by oxida-

tive polymerization as was shown in Figure 2.2 [26]. According to Kong and Yu, proteins

are evidenced by amide I signals at 1686, 1665, and 1645 cm−1(νC=O); and amide II

signals at 1547, 1522, and 1510 cm−1(δN-H, νC-N) [52, 55, 56, 57]. The band at 1510

cm−1also corresponds to the C=C interaction of aromatic amino acid ring modes [52, 28].

The lead-white presence in the sample is shown at 680 cm−1[16, 17, 26]. This pigment’s

effect in the painting is the loss of ester linkages and the weakened net yield of carboxylic

acids visualized at 1713 cm−1and broadband between 1622 and 1537 cm−1, attributed to

the formation of carboxylates, in this case, coordinated with lead [26]. Likewise, carbon-

ates associated with lead-white or metal carbonates are at 1396 cm−1with C=O stretching

[16, 17, 27, 61].

“San Agustın entre la Sangre de Cristo y la Leche de la Virgen”

The yellow color of the sample AM1SA, is possible to attribute to yellow ochre, a pigment

used around the 17thcentury reported on The Virgin’s apparition to Saint Martin, with

Saint Agnes and Saint Thecla, Eustache Le Sueur, France [59] and also Bolivian churches

[48]. According to Pavlidou et al. and Douma [54, 18], yellow ochre is a natural mineral

made of silicates (quartz, kaolinite) and clays owing its color to hydrated forms of iron

oxide, goethite (FeO(OH)) and mixed with gypsum [48]. In the spectrum of Figure

4.6 and Table 4.5, the band correspondent to kaolinite (alumino-silicate) at 1115(sh)

cm−1appears in the same band of gypsum. The other silicates and alumino-silicates are

present at 1033(s), 1003(s), 943(m), 918(sh), 796(w), 760(m), 698(m) cm−1. Also, the

presence of gypsum is observed at 671 and 601 cm−1. The other yellow ochre component

is the goethite; despite the prominent bands below 500 cm−1, it is possible to visualize in

fewer intensity signals at 894(sh) cm−1and 796(w) cm−1.

The broadband of νO-H around 3350 cm−1mask the N-H stretching of amides. The bands

at 2922(vs) and 2852(s) cm−1correspond to the C-H bond stretch of hydrocarbon chains


attributed to fatty acids and proteins commonly found on binders [17, 28, 26]. The main

C=O stretching feature band at 1729(s) cm−1and the shoulder observed by applying

the 2nd derivative at 1706 cm-1 is associated with free fatty acids formed by glycerol

esters’ hydrolysis degradation process [16, 27, 25]. Also, there are two bands at 1248 and

1219 cm−1(νC-O) due to triglyceride ester linkage caused by oxidative polymerization

[26]. Those carbonyl bands hint at lipid binder [27], possibly linseed oil, which is the

most commonly reported in the 17thcentury according to some art and historical studies

published [8, 11, 28, 31]. Evidencing protein binders is observed a shoulder at 1667

cm−1[17] and 1365 cm−1[25]. Also, according to Kong and Yu, there are bands of proteins

secondary structure at 1640 and 1605 cm−1for C=O stretching of amide I; and at 1514

cm−1(δN-H, νC-N) for amide II.

Figure 4.6: Infrared spectrum of the sample AM1SA.

Table 4.5: FTIR vibrational bands of the sample AM1SA. Symbols meaning: w= weak,vw= very weak, sh= shoulder, s= strong, vs= very strong, ν= stretching, δ= bending,

τ= twisting, ρ= rocking, as= asymmetric, and s= symmetric.


Wavenumber



νN-H Amide [52]

2922 vsνC-H (sp3) Hydrocarbon chains [17, 28, 26]

2852 s

1729 s νC=O Triglycerides [26, 27]

1706 sh νC=O Carboxylic acid [16, 28, 26]

1667 sh νC=O Amide I [52, 17]

1640 mνC=O Amide I [52]

νasCOO− Metal oxalates [16, 17, 27]


νC=C Aromatic [28]

1514 mνC=C Aromatic [28]

δN-H Amide II [52]

1449 s δCH2, δasCH3


[16, 53]

Terpenoids [11, 28]

1410 sh νC-O Carbonates [16, 17]

1391 s νasC-O Metal Carbonates [27]

1365 sh νC-OMetal Carbonates [16, 27]

Amide I [52, 25]

1311 s νsCOO− Metal oxalate [16, 26]

1248 mνC-O Triglyceride ester linkage [26]

1219 m

1165 s νC-O

Carbonates [16], Triglyceride

ester linkage [26], Terpenoids

[11, 28]

1115 sh νSi-Al-OHAlumino-silicates and gypsum

[27, 54]

1093 vs νC-O Terpenoids [11, 28]


1033 vs νSi-O Silicates [54]

1003 s νSi-O-Al Alumino-silicates [27, 54]

943 mνAl-OH Alumino-silicates [27, 54]

918 sh

894 sh νFeO(OH) Goethite [54]

796 wνSi-Al-OH Alumino-silicates [27]

νFeO(OH) Goethite [54]

760 m νSi-Al-OH Alumino-silicates [27, 54]

698 mρCO3− Metal carbonates [26]

νMg/Al-OH Alumino-silicates [27, 54]

671 s δCOO−Metal carbonates [17, 16]

Gypsum [54]

653 m Unidentified

623 s Unidentified

600 s Gypsum [54]

586 vs Unidentified

558 s Unidentified

Protein signals can relate them with animal glue, egg, or casein as the general protein

binders employed around the 17thcentury [17, 28]. Also, aromatic amino acid ring modes

are showed at 1605 and 1514 cm−1for C=C stretching due to protein media, which may

be from animal glue [28]. The bands observed at 1449, 1165, and 1093 cm−1may indicate

terpenoid resins like mastic resin, founded in studies of 17thcentury paintings from Poland

[28] and Belorussia [11]. Degradation products from organic materials, metal oxalates and

carboxylates appear at 1640 cm−1(νasCOO−), 1449 cm−1(δCH2, δasCH3), and a charac-

teristic signal of calcium oxalate (CaC2O4*H2O) at 1311 cm−1(νsCOO−) [16, 17, 27].

Other compounds found in the sample are carbonates and metal carbonates with a strong

band at 1391 cm−1(νasC-O), followed by 1365 and 1165 cm−1(νC-O) [16, 26]. Lead and

calcium carbonate show an intense absorbance at 1391 cm−1, whereas the second band

at 872 cm−1, only for calcite (CaCO3) [27]. The presence of these metal carbonates are


related to the 17th-century pigments generally applied at the ground layer as lead-white

(2PbCO3·Pb(OH)2) by Johannes Vermeer [13] and chalk (CaCO3) by Gdansk, who after

chalk use lead-white as a white pigment and not as a base for ground layer [28]. Then the

representative signals for lead carbonates are 1391(s) and 671(s) cm−1[16, 27], and also

shoulders observed by the second derivative at 1410 and 1365 cm−1[16, 17].

The red color of the cross-section R2SA is associated with red ochre, a pigment employed

around the 17thcentury, founded on wall paintings of Bolivian churches [48] and Europe

at Romanian, Poland, and French paintings [29, 16, 59]. Red ochre is a natural earth

pigment, it contains a mixture of minerals, clays, and quarts, and its red color is due

to anhydrous iron oxide, hematite (Fe2O3) [38]. Figure 4.7 and Table 4.6, show that

the bands at 1043, 1089, 1165 cm−1, and 806 cm−1(νSi-O) are associated with silicates.

At 935 cm−1(νAl-OH) and shoulders at 1019 cm−1(νSi-O-Si) and 1001 cm−1(νSi-O-Al)

correspond to alumino-silicates [27].

These silicates and alumino-silicates could be kaolinite and quartz, found as hematite

impurities [29]. Another impurity that can appear when red ochre is present is calcite

(CaCO3) [29]; the carbonate bands are at 1376 cm−1and around 1410 cm−1. The bands

of silicates (quartz) and red ochre match at 1165, 1089, 806, and 690 cm−1, some of

those bands could be overlapped by the νC-O of triglyceride ester linkages of oils. Also

is possible to make a relation between the presence of hematite and the degree of oil

oxidation. Hematite can retard the oxidative polymerization of oils, which can be proved

with the absence of a band around 1776 cm−1[26]. The band at 1741 cm−1is associated

with vegetal oil and its oxidation produces broadband, or near new bands, which are not

observed. Taking all these facts is possible to assume the use of red ochre in this part

of the painting. The O-H stretching at 3378 cm−1is overlapping the N-H vibration from

amides. The C-H bond stretches of hydrocarbon chains from fatty acids and proteins

are observed at 2923 and 2853 cm−1[28]; C-H bending at 1462 cm−1[38, 25], and 726

cm−1(τC-H).


Figure 4.7: Infrared spectrum of the sample R2SA.

Table 4.6: FTIR vibrational bands of the sample R2SA. Symbols meaning: w= weak,vw= very weak, sh= shoulder, s= strong, vs= very strong, ν= stretching, δ= bending,


Wavenumber


3378 wνO-H Hydroxyl group

νN-H Amide [52]

2923 vsνC-H Hydrocarbon chains [17, 28, 26]

2853 m

1741 m νC=O Triglycerides [26, 27]

1710 sh νC=O Carboxylic acids [16, 28, 26]

1663 sh νC=O Amide I [52]

1644 w

νC=C Aromatic [28]

νC=O Amide I [52]

νasCOO−


1605 w νC=C Aromatic [28]

1512 wνC=C Aromatic [28]

δN-H, νC-N Amide II [52]

1462 m δC-H Aliphatic chains [38, 25]

∼1410 νC-O Carboxylates [26]

1376 w νC-OCarboxylates [26]

Terpenoids [11, 28]

1283 mνC-O Triglyceride ester linkage [26]

1257 m

1165 m

νSi-OSilicates [27]

νC-O

Triglyceride ester linkage [26]

Terpenoids [11, 28]

Carbonates [16]

1089 s νC-O Terpenoid [11, 28]

1043 m νSi-O Silicates

1019 sh νSi-O-Si Silicates - Kaolinite [27]

1001 sh νSi-O-Al Silicates - Kaolinite [27]

925 m νAl-OH Alumino-silicates


726 m τC-H Vegetal oil [38]


673 m δCOO− Carbonates [17, 26]

The bands at 1741, 1283, 1257, and 1166 cm−1correspond to the C=O stretching of

triglyceride ester linkages critical to oxidative polymerization [17, 26, 27]. The second

derivative allows visualizing a shoulder at 1710 cm−1nd the C-O stretching vibration at

1420 cm−1and 1376 cm−1suggesting the formation of carboxylic acid products, carboxy-

lates [26]. Those carbonyl groups are related to the presence of vegetal oil in the sample,

and the oil could be from linseed, which is the most founded in artwork studies in the

17thcentury [8, 11, 28, 31].

According to Kong and Yu [52] the presence of amides from protein binders (egg, casein,


animal glue) [11, 17, 28], is confirmed by the bands at 1663 and 1644 cm−1(νC=O) for

amide I, and at 1511 cm−1(δN-H, νC-N) for amide II, which are the most observable bands

belong to protein secondary structure [55, 56, 57]. Additionally, the C=C vibration of

aromatic amino acid ring modes are present at 1605 and 1512 cm−1[52, 28]. Terpenoid

resins (mastic and others) found on European paintings in the 17thcentury [11, 28] could

be associated with absorbance at 1376, 1165, 1089 cm−1. Degradation products from

organic materials are at 1643 cm−1(νasCOO−), a signal attributed to oxalates [16, 17].

A central band shows carbonate compounds at 1165 cm−1(νC-O), and metal carbonates

may be from lead-white and its presence at 1043 and 673 cm−1(δCOO−). Lead-white

is one of the most used pigments based on the ground layer or only as a white pigment

during 17thcentury [13, 28, 16, 17, 27].

In the spectrum of the sample ESA in Figure 4.8 and Table 4.7, the top bands are observed

at 1042 and 1095 cm−1(νPO3−4 ) suggests the presence of calcium phosphate Ca3(PO4)2,

the main component of Bone black [38]. Other complementary bands of phosphates with

less intensity at 803(m) cm−1. It is a black pigment, formed mostly of Ca3(PO4)2 and in

less amount of C and CaCO3, used around 17thcentury, if this deteriorates, it could appear

as white stains [31]. Silicates and alumino-silicates are found at 1118 cm−1(νSi-Al-OH),

1004 cm−1(νSi-O-Al), 939 cm−1(νAl-OH), and 916 cm−1(νAl-OH), possibly due to quartz

or kaolinite, which are considered as impurities due to the use of ochre pigments such as

red and yellow [29, 27, 54].

Around 3408 cm−1the broadband of O-H is overlapping the N-H signal of amides. The

C-H bond stretching of hydrocarbon chains from free fatty acids and proteins are shown

at 2958, 2922 and 2853 cm−1[28] with C-H bending at 1467 cm−1(2nd derivative) and 1371

cm−1[25], the deformations of C-H in –CH2- and -CH3 at 1452 cm−1[28], and C-H torsion

at 752 cm−1[38]. The main band at 1727 cm−1and the shoulder at 1710 cm−1observed by

the second derivative correspond to the C=O stretching of additional ketone, ester, and

acid carbonyls formed during the oxidative polymerization [26]. Those carbonyls are the

evidence of vegetable oils present in the sample, possibly linseed oil, which is the most

common in the 17thcentury [8, 28, 31].


Figure 4.8: Infrared spectrum of the sample ESA.

Table 4.7: FTIR vibrational bands of the sample ESA. Symbols meaning: w= weak,vw= very weak, sh= shoulder, s= strong, vs= very strong, ν= stretching, δ= bending,


Wavenumber


3408 wνO-H Hydroxyl group

νN-H Amide [52]

2958 sh

νC-H Hydrocarbon chains [17, 28, 26]2922 s

2853 m

1727 m νC=O Triglycerides [26, 25]

1710 sh νC=O Carboxylic acid [28]


νasCOO− Oxalates [17]

1603 shνC=O Amide I [52]


νC=C Aromatic [28]

1546 m δN-H, νC-N Amide II [52]

1517 mδN-H Amide II [52]

νC=C Aromatics [28]


1452 sC-H deformation


1419 shνas(CO2−

3 ) Carbonates [16, 17, 26]1401 s


1320 mνC-O


[27, 53]

νsCOO− Metal oxalates [17]

1282 m

νC-O Triglyceride ester linkage [17, 26]1260 m

1154 m

1118 s νSi-Al-OHAlumino-silicates and gypsum

[27, 54]

1095 s νPO3−4 Bone black [38]

1042 sνPO3−

4 Bone black [38]

νsC-O Carbonates [17]

1004 sh νSi-O-Al Kaolinite [27]

939 mνAl-O-H Kaolinite [27]

916 w

803 m νPO3−4 Bone black [38]

752 m τC-H Vegetal oil [38]

676 s δCOO− Carbonates [16, 17]

Also, there are bands due to triglyceride ester linkage caused by the oxidative polymeriza-

tion at 1282, 1260, and 1154 cm−1(νC-O) [26]. Verifying the presence of protein binders, at

1644 cm−1(νC=O) is the absorbance by amide I; and at 1546 and 1517 cm−1(δN-H, νC-N)

for amide II [52], belong to proteins secondary structure [55, 56, 57]. The popular binders


used around the 17thcentury were casein, egg, and animal glue [11, 17, 28]. Those protein

binders could contain amino acid rings, observed at 1603 and 1517 cm−1(νC=C) [52, 28].

The oxalates signals are observed at 1644 cm−1(νasCOO−) and 1320 cm−1(νsCOO−), due

to calcium oxalate as a degradation product of organic materials [17]. The presence of

lead-white, commonly used in the 17thcentury in the ground [5, 6], could be related to

the carbonates and metal carbonates bands at 1419, 1401, 1042 and 676 cm−1[16, 17].

4.2.2 Raman Spectroscopy

The yellow cross-section, AM1SA, reveals bands observed at 79, 128 and 195 cm−1in

Figure 4.9, those are reported as representative of the pigment Lead-tin yellow type I

[45, 50], which has been used around the 17th century according to Sandalinas and Ruiz-

Moreno [45]. This pigment was also found in G.B Langetti and Luca Giordano’s paintings,

Italian painters [45, 47].

Figure 4.9: Raman spectrum of the sample AM1SA

4.3. Ancient Pigments 45

4.3 Ancient Pigments

4.3.1 Carmine lake

According to Parrilla Bou [49] and Douma [18], carmine as a pigment is founded mixed

with alum. To prove the pigment’s presence in some of the samples was necessary to take

the infrared spectrum from cochineal dye, cochineal with alum, and alum. Due to the

samples’ high complexity, identifying the presence of carmine lake results in difficulty due

to overlapping with the other painting components and the influence of environmental

conditions. Then, it is necessary to determine marker bands of the possible element. In

this case, alum could be the unique compound present. Then, as shown in Figure 4.10,

the marker band for alum is around 580 cm−1. If this is founded on the samples’ infrared

spectra, it is possible to assume that carmine lake was present. However, the organic part

(carminic acid – cochineal) had disappeared and is not possible to identify due to the

time effect. The suspected samples with carmine lake were the red ones, but the organic

component or any hint to assume this dye’s presence could not identify in them. Due to

the complete degradation of an organic compound by the time or a minimum content of

this compound, it may be overlapped by other elements.

Figure 4.10: Infrared standard spectrum. (a) Cochineal, (b) Cochineal with alum, and(c) Alum.


4.3.2 Yellow Saffron

There are no specific reports of the found of yellow saffron in paintings; nonetheless, his-

torically, this dye has been commercialized as an orange dye during the 17thcentury in

the territory now known as Ecuador [9]. Comparing saffron standard with both yellow

samples showed in Figure 4.11, was impossible to identify its presence in the samples, con-

sidering the spectra’ complexity. There are many overlapped bands eluding the detection

of this component.

Figure 4.11: Infrared spectra of (a) AM1SA, (b) FASG, and (c) Yellow Saffronstandard.

Table 4.8, as a summary, presents the main painting components associated with the

samples analyzed in this work by ATR-FTIR and Raman spectroscopy. The results are

organized by sampling area (yellow, red, and flesh-colored) and artwork name. This table

gives a general outlook of Miguel de Santiago’s palette and painting materials related

to the 17thcentury, according to Table 2.1. The materials which not correspond to the

17thcentury are a probable hint of restoration achieved from the era of the materials used.


Table 4.8: Summary of results.

SampleAgustın se presentaen una vision a SantaGertrudis

San Agustın entre laSangre de Cristo y laLeche de la Virgen

Yellow

Bone black Yellow ochreVegetal oil (linseed) Lead-tin yellow type I*Protein binder GypsumLead white Protein binderYellow ochre Vegetal oil (linseed)

Lead white/calcite

Red

Cellulose or starch Red ochreRed ochre Calcite/Lead whiteVegetal oil (linseed) Protein binderProtein binder Vegetal oil (linseed)Calcite/Lead white Resins (terpenoids)

Flesh colored

Bone black Bone blackOchre pigments Ochre pigmentsVegetal oil (linseed) Vegetal oil (linseed)Protein binder Protein binderLead white Lead white

* Raman spectroscopy

Chapter 5

Conclusions and Recommendations

5.1 Conclusions

This work sets out to determine the pictorial components used by Miguel de Santiago in

two of his attributed paintings. The following was found:

• Through infrared spectroscopy, it was possible to identify, in both artworks, the

presence of yellow ochre, red ochre, and a mixture of the two in the yellow, red,

and flesh-colored samples respectively. Bone black as a pigment was found inside

flesh-colored samples of both paintings and in the yellow sample of the painting

“Agustın se presenta en una vision a Santa Gertrudis.”

• The pigment lead-tin yellow type I was detected through Raman Spectroscopy in

the sample taken from “San Agustın entre la Sangre de Cristo y la Leche de la

Virgen.” Unfortunately, due to the fluorescence of organic compounds present in

the other samples, it could not gain further information using Raman spectroscopy.

• Ancient pigment recipes for carmine lake and saffron were recreated to determine

if they were used in the artwork. Given the limitations of this study, it focused

on looking for alum on red samples to confirm or discard the use of carmine lake

(ancient pigment recipes for carmine lake always contained alum). Given the absence

of alum, it was concluded that carmine lake was not present in the samples analyzed.

In yellow samples, saffron’s presence could not be confirmed given the complexity

of overlapped signals in the sample’s spectrum.

• In the red sample of “Agustın se presenta en una vision a Santa Gertrudis,” the pres-

ence of carbohydrates was detected, and it was able to narrow it down to cellulose

or starch.

• All samples contained linseed oil and proteins as binders, and the red sample of “San

Agustın entre la Sangre de Cristo y la Leche de la Virgen” also contained terpene

resins as a binder.

• In the ground layer, painting materials lead-white and calcite were found in all

analyzed painting samples.

48

5.2. Recommendations 49

After the extensive literature review about Ecuadorian cultural heritage done as a part

of this study, it was found that there is not much work focused on Miguel de Santiago’s

palette identification. There is no academic work at present using vibrational spectroscopy

techniques, making this research pioneer in the field.

5.2 Recommendations

These are recommendations for future works:

• To determine if cellulose or starch were used as binders, it is necessary to employ

other complementary techniques such as Polarized light microscopy (PLM). If the

binder turns out to be starch, this could be evidence of a restoration done on the

artwork after the 18thcentury.

• Further analysis, thought destructive techniques such as High performance liquid

chromatography-mass spectrometry (HPLC-MS), could shed more light on identi-

fying organic compounds such as carmine lake and yellow saffron used extensively

in 17th-century artwork.

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