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The Gum Bichromate ProcessThe Gum Bichromate Process

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OVERVIEW AND EXPECTATIONSAt first glance, the gum bichromate process looks amazingly uncomplicated. However, to nearly every one of my students who has been seduced by the process, and for those artists who are dedicated to it, gum is one of the most complex in the alternative genre. Gumbichromate printing is certainly seductive due to its limited chemistry, simple waterdevelopment, and unlimited color potential with watercolors of the artist’s choice. Gumprinting is quite flexible and easily combined with other processes and graphic disciplines.Because of its pigment, paper, and brush roots, gum bichromate is one of the few photographicprocesses capable of achieving that wonderful element of gesture—gesture being that painterlyexpression of the “artist’s hand” in the creation of a mark.

In this chapter I, as always, give you a little history and describe how the process works. Ithen discuss the negative and a technique, euphemistically referred to as registration, that willallow you to place multiple applications of color on the same piece of paper without losing theoriginal sharpness of the image. You will also learn how to make a gum print from a singlecontact negative.

You’ll learn about mixing the chemicals for the sensitizer and the relationship among thethree primary ingredients in the technique: gum arabic, a dichromate sensitizer, and watercolorpigment. This is followed by instructions for applying the coating, processing, and thereapplication of the sensitized coatings. A discusion about development and clearing gum prints is included, and the chapter concludes with a comprehensive trouble-shooting section.

Figure 13–1Christopher James, Grace in Gum, 1977This is from a series of gum bichromate portraitsthat I made from damaged internegatives that hadbeen thrown in the trash in the Harvard photogra-phy labs. The final negative was enlarged on SO-339 direct duplicating film (now SO-132) and thenabused for several days with gum bichromateapplications, paint, ink, dyes, bleaches, and etch-ing tool abrasion in wet emulsion.(Courtesy of the author)

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Considering the surface simplicity of the process, you’llnotice that there is a lot of information to absorb, and Iwant you to see that the variables within gum printing areinfinite. If you investigate the process beyond this bookyou will find published evidence that will occasionallyseem contrary to portions of the information in this chap-ter. Some of that information will work quite well for you,whereas morsels of other instruction will not work for youwith equal success. In gum printing there are very fewabsolutely correct ways to do anything, and much of whathas been previously published has simply been the proce-dure of choice for the individual teacher or author. In myexperience, gum bichromate printers are the most pas-

sionate and stubborn of all alternative process artists whenit comes to their particular way of doing the process. I canjust imagine many of my friends reading that last sentenceand saying, “He’s talking about me!”

You’ll find that you’ll be able to make excellent gumprints using, and adapting, the instructions in this chap-ter. Just relax, keep notes of what you are doing, and real-ize that the gum process will reward you if you work at itwithout a need for instant gratification. Have a great timeindividually modifying the myriad elements of the tech-nique to suit your own personal working style, imagery,and intentions.

Figure 13–2Robert Demachy (1859–1937), Cigarette Girl(Gum bichromate print reproduced as aphotogravure in Camera Notes, Vol. 6, No. 1,July 1902)Robert Demachy was an artistic force in the1880s and began to interpret his work in gum in1894, because it allowed him to use consider-able handwork and was similar to the feelingshe had when looking at Impressionist paintings.Demachy founded the Photo-Club de Paris andwas a stalwart member of the Linked Ring aswell as an honorary member of the RoyalPhotographic Society. In spite of his success,Demachy completely divorced himself fromphotography in 1914.(Courtesy of the George Eastman House, Rochester,NY)

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A LITTLE HISTORYAn interesting hypothesis from a book by Picknett andPrince entitled, Turin Shroud—In Whose Image? The TruthBehind the Centuries-Long Conspiracy of Silence (AcaciaPress, 1994) suggests that Leonardo da Vinci (1452–1519) may have been the creator of the Shroud of Turinby using a mixture of dichromated egg with human or ani-mal urine. Guess whose image is on the Turin shroud? —why, it’s da Vinci’s self-portrait, of course. The book’sauthors, if correct, would give Leonardo da Vinci creditfor the first photographic image several hundred yearsbefore the medium’s “official” beginning. To put this curi-ous factoid in context, the publisher’s catalogue is rife withbooks dealing with conspiracy theories dating back to thefourteenth century. Who knows? Considering everythingelse da Vinci accomplished, it might be true.

Collotype: CalotypeThe Collotype is a photomechanical/lithographic-likeprocess invented by Alphonse Louis Poitevin (1855) inwhich a pane of ground glass is coated with a bichro-mated gelatin. The coated glass is next baked to createa fine reticulated (grainy-mezzotint-like) surface. Thebaked glass is next exposed to a negative under UVlight, and the bichromated gelatin hardens in proportionto the exposure, as in a gum bichromate print. The plateis then washed, so that the unexposed/unhardened gel-atin washes out, and then coated with glycerin. Theglycerin coating allows the remaining bichromate to behygroscopic (able to absorb moisture from the air) in pro-portion to the degree of the bichromate’s exposure. Tomake a print, the plate is rolled with greasy lithogra-pher’s ink; the ink adheres to the exposed areas of theplate with the least water content, and then printed onpaper. Commercial usage was common following theperfection of the process by Joseph Albert in 1868.The Calotype, invented by William Henry Fox Talbot in1835, is the name for the first photographic process toproduce a negative that would facilitate the making of adirect positive. In the Calotype process a piece of high-quality writing paper is sensitized with a solution of sil-ver iodide: potassium iodide and silver nitrate. Prior toexposure, a second solution of silver nitrate, acetic acid,and gallic acid is applied to the paper (increasing thelight-sensitivity), dried, and exposed to UV light. Theexposed image is then resensitized with a solution ofgallo nitrate of silver (gallic acid and silver nitrate) thatcauses the latent image to emerge. The print is thenfixed in a solution of potassium bromide or sodium chlo-ride, and after it has dried, used as a negative (some-times waxed, or oiled, to enhance the transparency ofthe paper negative) in contact with a newly sensitizedpiece of paper to produce a direct positive. This process,following some improvements, was renamed the Talbo-type and is, in current definition, much like a salted paperprint. In 1844, Talbot published the second photograph-ically illustrated book, The Pencil of Nature, hand tippinghis Calotypes throughout the manuscript.

Figure 13–3Cover of Issue # 3, The Pencil of Nature, 1844(Courtesy of the Royal Photographic Society)

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The earliest attributable thinking about the effect oflight on bichromates seems to be the property of theFrench chemist Louis-Nicolas Vauquelin (1763–1829), atthe end of the 1700s. Although Vauquelin published over378 separate dissertations on chemistry, the bulk of hiswriting did little more than provide analytical observationsand data. Interestingly, he was one of the first academicsto consider instructing his students by means of actual,hands-on practice in the laboratory.

Mongo Ponton (1801–1880), the Scottish inventor(with the all-time best name in the history of photogra-phy), expanded on Vauquelin’s analytical wisdom in 1839

when he discovered that paper impregnated with potas-sium bichromate was sensitive to light. Ponton modestlychristened his discovery the Pontontype. In Ponton’sprocess, paper was coated with a potassium dichromatesolution and exposed to sunlight using objects to createa negative image. The exposed print was then washed, toremove any unexposed dichromate, and dried, leaving asepia brown positive image that consisted of chromiumdioxide. The print was rather handsome at first but tendedto fade to a gossamer-like green after several months.Ponton’s single solution Pontontype is directly related tothe idea behind Poitevin’s Dusting-On process (1858) anda sizing technique for liquid emulsions on paper, both ofwhich are covered later in this text. A year later, in 1840,Edmund Becquerel (1820–1891) added to this rapidlyexpanding base of knowledge by producing images usingstarch in combination with iodine. It was Becquerel, bythe way, who first figured out that Daguerreotypes couldbe supplementally intensified by the continuation of theDaguerreotype’s exposure through a red glass filter.

In 1854, William Henry Fox Talbot began workingon the concept by observing the ability of potassiumdichromate to have a hardening effect on a colloidal gel-atin that was directly proportional to the degree of UVlight that the gelatin received. Fox Talbot’s modest successin this area was followed by the work of Alphonse LouisPoitevin (1819–1882), who continued the investigationof how bichromates were able to render gelatin insolubleon exposure to light. In 1856, Honoré d’Albert, Duc deLuynes, an exceedingly wealthy arts patron, put up a prizeof 10,000 francs to anyone who could describe a photo-graphic printing process that was permanent. Poitevinwon the prize for two processes: the Carbon Print and theCollotype.

The Collotype, like others within the genre, that is, theWoodburytype, which utilized the unique hardening qual-ity of bichromates and colloids on exposure to ultravioletlight, was a significant achievement and provided a newway to reproduce photographic images in quantity. Theonly serious drawback to these techniques was that hand-set typography in a “chase” (a wood and metal device usedby typographers for blocking, setting, and locking type forinking and subsequent printing) and the photographicimage could not be printed simultaneously. It was not

Figure 13–4Antoine Francois Jean Claudet (1797–1867), Woman, 1844(Salted paper print from a Calotype negative)Claudet learned the Calotype process from Talbot but bemoaned the factthat it was too slow and less perfect than the Daguerreotype that he hadlearned from Daguerre. Claudet was a very active photographer and wasresponsible for the first red safelight in the darkroom and the concept of asequence of images to express movement.(Courtesy of the National Museum of Photography, Film andTelevision/SSPL)

until the 1880s, with the advent of the halftone (the dotpatterns in magnified press reproduction) plate, that thislimitation could be addressed.

From the same time period, the French painter Jean-Baptiste-Camille Corot (1796–1875) tried his hand atprocesses utilizing bichromates and colloids and madecliché-verre prints on glass using pure albumen as his siz-ing agent (see Figure 2–16). He also made colloidal etch-ings by coating glass plates with wet sensitized collodionemulsion. The plate was exposed to light, which darkenedthe entire plate. Corot then etched into the darkenedemulsion and, when finished, contact printed the plate toa piece of sensitized paper for a paper print. Corot andothers also utilized a technique in which they would burna tallow candle close to a glass plate, leaving a soot-black-ened sheet of glass. The soot was then drawn into with avariety of art-making tools to create a negative plate oflines and textures. The etched soot on the glass was thenused as a contact negative in conjunction with a sensitizedsheet of paper.

In 1895, John Pouncy (1820–1894), a gentleman pri-marily remembered for his photographic illustrations deal-ing with Thomas Hardy’s (Return of the Native) home turfof Wessex, gathered everyone’s information and claimedto have produced the first consistent and satisfactory gumbichromate printing process. Pouncy published Dorset-shire Photographically Illustrated in 1857. This book,despite criticism that it lacked halftone characteristics, wasthe first British book illustrated by means of photo-lithography. C

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Figure 13–5Nadar (a.k.a. Gaspard Félix Tournachon), 1820–1920, Portrait of GeorgeSand, 1877 (from Galerie Contemporaine, littéraire, artistique)Nadar had a brief, but stunning, career as a photographer in the mid-1800sprimarily due to his extraordinary social connections within the Frenchartistic and literary circles. His list of occupations and interests includedpoacher, freedom fighter, smuggler, cartoonist, and proponent of heavier-than-air flying machines. His photographic studio became the main officefor the Society of the Encouragement of Ariel Locomotion By Means ofHeavier Than Air Machines. Nadar was the president, and Jules Verne wasthe secretary. This is a Nadar Woodburytype of his friend and novelist,George Sand, who is remembered for her notorious affair with Chopin, herwardrobe of men’s clothing, her feminist politics, and for writing eightynovels about love, nature, and morality.(Courtesy of the George Eastman House, Rochester, NY)

Woodburytype (a.k.a. Photoglyptie –Stannotype – Photomezzotint)Walter Bentley Woodbury (1834–1885) created theWoodburytype in 1864—a process that was widely prac-ticed for nearly 25 years and known for its amazing ren-dition of values and tonal range without grain. Toproduce a Woodburytype, the artist would make a thickgelatin relief on a piece of carbon paper by exposing itto a continuous-tone negative. The relief image wasdried and then squashed into a lead intaglio plate underenormous pressure from a hydraulic press. The lead,having taken the detail of the hardened gelatin impres-sion, would now become the printing plate for the nextstep. The lead intaglio plate was encased in a mold andpressed against a fine-quality paper. Pigmented gelatinink was then poured into the mold, where it depositedthe gelatinized ink in proportion to the depth of the plate.The Woodburytype is generally a dark reddish browneven though any color could have been used. Interest-ingly, it was seldom printed in black.

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In the late nineteenth and early twentieth centuries,photographic image makers saw themselves as dedicatedartists rather than scientists, and some referred to them-selves as Pictorialists.They worked extensively with the gumprocess due to its innate ability to express the artist’s inten-tions and feelings. For critics of the movement this indi-cated that the imagery was warm, romantic, and fuzzy.Gum printing was a technique that was championed inAmerica by the Photo-Secessionists, a coalition of photog-raphers (Steichen, Käsebier, and White, and in due time,Steiglitz) who were dedicated to pictorialist, and individ-ual, expression in the medium. Their inspiration camefrom the aesthetic integrity of European organizationssuch as the Wiener Kamera Club (Berlin) and the Broth-erhood of the Linked Ring (London), who battled to havephotographic art appreciated within its own context ratherthan as an imitative reflection of informational reality.

How Gum Bichromate WorksPouncy had come to a conclusion, the underlying princi-ple being: a mixture of a potassium, or ammonium,bichromate salt (dichromate and bichromate describe thesame thing) in solution is mixed with a colloid such asgum arabic, gelatin, glue, or starch. This UV light-sensi-

tive liquid mixture is then applied to a substrate such aspaper, and dried. A contact negative, the same size as thefinished print, is placed on the dried sensitized coating ina contact printing frame and exposed to a UV light sourcesuch as sunlight. The portions of the sensitized paperaffected by UV light through the negative will becomeinsoluble in direct proportion to the amount of lightreceived.

By itself, the dichromated salt and the gum arabic (sapfrom an Acacia tree) will produce a tan-colored image.This particular solution is sometimes employed as a pre-liminary sizing layer for hand-applied liquid emulsionsand was referred to in Chapter 12. If a coloring agent,most often watercolor pigment, but occasionally a gaucheor a metallic powder, is added to the sensitized mixture,the color will remain in the UV light-hardened emulsion.

The dichromate/pigment/gum arabic mixture will, asI’ve said, harden in direct proportion to the degree of UVexposure received. In a first exposure, the thinnest partsof the negative (shadows) will allow the most exposure andcause the image on the coated paper to become the mosthardened in those areas. The densest parts of the negative(highlights), which require more exposure, will permit lesshardening. The exposed print is then “developed” in water,whereupon the hardened gum/pigment remains on thepaper in proportion to the exposure, the dichromate sen-sitizer-to-pigment ratio, and the amount of pigment in themix. The less-exposed areas will clear in the developmentin proportion to their exposure, leaving the highlightsclear and the middle values open in relation to the aboveand other factors, which include paper, water, and painttype and how these work with the chemistry and indi-vidual technique.

A Few Words Before We BeginAny change in the principal components of the gumprocess (gum type, sensitizer type and strength, ratios ofboth to one another, water type, temperature, paper, timeof year, etc.) on any given day, may change the final resultsyou will get in a gum print. This is exactly what makesthe process so interesting as long as you avoid investingyour self-worth and abilities as an artist on guaranteed suc-cess. Be patient and don’t try to conquer the process. Myfriend Judy Seigel has probably spent more time and

The Fish-Glue ProcessAs an aside, there was a technique known as the “FishGlue Process” that used these same principles butapplied them for use on a metal plate substrate.Alphonse Louis Poitevin is credited with the invention ofthis process. In the Fish Glue Process, ammoniumbichromate and water-soluble fish glue were mixed andcoated on a metal plate. Following exposure, the unhard-ened glue (acting like the gum arabic) washed off theplate and was then heat hardened. The heat hardeningproduced an enamel-like surface that was subsequentlyacid etched and used in a press to make a bas-reliefimage. Fish glue is still being manufactured and can bepurchased, should you get an urge to try this seldom-used technique. See Appendix E of this book for a sup-plier of fish glue.

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energy exploring the variables of this technique than any-one I know, and she is still occasionally coming face-to-face with unexpected information and imagery. It wouldbe a “fool’s errand” to try to conquer this process in a shorttime. Judy provides some decent advice when she suggeststhat one can come to a working truce just by payingattention. The gum bichromate process is amazingly fluidand flexible and should be approached with a spirit of play,adventure, and discovery.

The Gum Negat ive

Because gum bichromate is a contact printing process itis necessary to have an enlarged negative(s) to work withthat will be the same size as your final printed image. Themajority of gum printing experiences requires more thana single exposure; multiple applications of sensitized colorare the norm. For this reason, it is common to have a setof registered negatives that will allow you to print good

Figure 13–6Karen Fiorito, Study for My Voice, 1997Karen was a former student of Sarah Van Keuren’s at the University of the Artsand, according to Sarah, one of the firststudents there to combine digital andalternative process. Karen first made adigital print, printed it out, and then made a lith negative of the print using a copycamera. The lith negative was then used to generate the gum print.(Courtesy of the artist and SVK)

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highlights, midtones, and shadow details. If your inten-tion is to have a single color gum, with many applicationsof the same color, one negative may be all that you willrequire. With a single negative, all one has to do is adjustthe components, such as the concentration of pigment,exposure, and amount of sensitizer in order to make aresolved image.

It is advisable to have negatives that would be appro-priate for a normal grade of silver gelatin paper. Thismeans that the negative will have an average negative den-sity of 1.0 to 2.0. This is a general suggestion unless youintend to make gums for interdisciplinary intentions,where the tonal values are secondary to the concept. If youare looking for a full tonal range, and gum is more thancapable of giving this to you, it is best to avoid negatives

that are too high in contrast—unless, of course, that iswhat you’re looking for.

There are a host of film varieties and developers avail-able for nearly any type of negative interpretation you arewishing for. Recently, in workshops where timing is tight,I have been separating transparencies in separate CMYK(C= cyan, M= magenta, Y= yellow, K= black) files in Pho-toshop and printing them out on acetates on a quality ink-jet printer. CMYK separations are decent negative optionsand eliminate the need for darkrooms or the time andmoney required for dealing with a service bureau. Most ofthe time, digital negatives are perfectly satisfactory for gumsand offer you flexibility and speed in negative reproduction.You may also wish to consider using negatives made fromlaser copy machines or making your own with a cliché-verre

Figure 13–7Judy Seigel, Jesus Singers(Single coat gum bichromate with acrylicborder)Judy Seigel has been a champion influence inthe renewed interest in alternativephotographic processes. Her specialty is gumbichromate, and her passion for the alternativeimage is unflagging.(Courtesy of the artist)

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technique. (Refer to Chapter 2, “The Negative,” and Chap-ter 3, “The Digital Options,” for more information.)

Regis t ra t ionRegistration is done after sizing and hardening. If youintend to make multiple passes or if you are working ona more complex gum, such as trying to duplicate a colortransparency from four CMYK separations, it will be nec-essary to register your negatives. If you don’t register them,you will quite often get curious and unexpected results.This accident may well be a “good” technique if you useit intentionally.

There are many ways to register negatives and paper.Some of the methods include paper punches, pushpin

holes, stick-on transparent registration targets appliedduring negative production, or an old dye transfer punch-board. You can also register simply by laying your coatedpaper on a light table, quickly registering your negativesto the sensitized paper, and locking it in pieces of trans-parent tape. Don’t stress about the light from the lighttable. Even though your dried emulsion is sensitive tolight, you still have plenty of forgiveness in the emulsionspeed and will have time to secure the registration with-out fogging the image. The point of registration is to giveyourself a repeatable and mechanical way of accuratelyaligning your negative, or a different one, on the samepiece of paper. This is especially true when a different coloris assigned to each negative and where it is difficult to seethe base image after recoating.

Figure 13–8John Quackenbos, Four color gum bichromateprint made from digitally separated negatives,1999This gum bichromate print was generated fromthe CMYK separations in Figure 3–15 throughFigure 3–18, which come originally from a 35 mm transparency (Figure 3–14) of my 1999Maine Photographic Workshops alternativeprocess class making a cyanotype mural.(Courtesy of the artist)

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One Example of a Simple Registration TechniqueOn a light table, register all of the negatives to be used inyour print. With a mat knife or sliding blade paper cut-ter, trim the margins at different lengths of all but one neg-ative so that when they are in registration each piece offilm will have a different height but will still be in regis-tration with the others. Run a strip of tape across thepacket of trimmed edges so they can be picked up as a set.

When this is done, place the packet of taped negativeson the area of your sized paper that you will be printingon. Move the sized paper and the taped negative pack toa clean surface that will accept a pushpin and poke a pin-hole through two or three margins of the negative set andpaper. These holes will serve as your registration referenceguides later on. Of course, if you wish to have a lot morecontrol, then your registration techniques will have to bea lot more sophisticated than what I’ve described above.If you have a strong urge to make this process more com-plicated, please feel free to do so.

The Components in a Gum EmulsionThe emulsion for gum bichromate printing is prepared insimple and separate steps. Begin by mixing your dichro-mate solution. Most gummists use either potassium orammonium dichromate, but it is also acceptable to usesodium dichromate, although I don’t know anyone whodoes. Potassium dichromate tends to be a bit slower than

ammonium dichromate but generally clears out in thehighlights a little better than does ammonium. Whicheversensitizer you elect to use is added to a mixture of gumarabic and watercolor paint to make the complete solu-tion for coating. Additional water can also be added andwill help make your emulsion smoother. The proportionsof gum arabic to sensitizer can be adapted to suit your con-trast and exposure time requirements as well. Some gumpractitioners also substitute a liquid glue (like Gloy®), oralbumen, for the gum arabic. I hope you can begin to seethat the process is not one where hard and fast rules apply.

The Ammonium/Potass ium Dichromate Sens i t i ze rAmmonium or potassium dichromate is your sensitizerand is added to your mix of liquid gum arabic (with a spe-cific gravity of 12˚ to 17˚ Baumé) and watercolor pigmentwhen you are ready to make an exposure. It is a typicalalternative emulsion, suitable only for contact printingunder UV light. You don’t have to worry very much aboutworking with it under normal low-light conditionsbecause it doesn’t become truly light-sensitive until it isdry. I once gave a workshop demonstration in gum print-ing in a motel lobby where we hung the motel’s yellowsheets over sun-filled windows and there was no problemwith fogging. I performed another gum demonstration inthe back of a van in a parking lot on a rainy day and had

Figure 13–9Mary Pat McNally, Mixed Fruit #6, 1996Mary Pat did a series of four color gumbichromate pieces for her senior thesis atthe Art Institute of Boston. The negativeswere CMYK separated in Photoshop® andtranslated in true-to-life color. It was thefirst time I had seen a student use thecomputer solely as a tool for a uniquealternative process, and her successdemonstrated to me the importance ofincorporating digital technology as analternative process component.(Courtesy of the artist)

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no problems there either. Avoid excessive fluorescent lightas you would with other alternative processes.

Making a Working Saturated Solution ofAmmonium or Potassium DichromateDichromates are used in a saturated solution. A saturatedsolution is defined as one where no more of the chemicalcan be dissolved in water without leaving a sediment. Asmentioned earlier, ammonium dichromate is saturated ataround 25% to 30% and potassium dichromate at 10%to 13%. Ammonium dichromate is more sensitive thanpotassium dichromate (due to more dichromate ions inthe solution), but the only differences that you notice willbe that exposure time will be shorter with the ammoniumdichromate. The contrast, all things being equal, will bethe same, but you may experience an easier time clearingthe print with potassium as your sensitizer. Again, one fac-tor will impact another and you’ll need to work out yourown system to accurately predict outcome.

If you decided to use potassium dichromate as yoursensitizer, make a saturated solution of it. For the purposeof simple explanation we’ll use a 10% solution as our goal.Knowing that potassium dichromate is in a saturatedsolution at 10%, take a digital or triple beam gram scale,weigh out 10 g of potassium dichromate, and stir it intosolution in 100 ml of water. This makes a 10% workingdichromate solution. There is a range here, and if youopted to make a saturated solution of 13% then youwould be using 13 g to the 100 ml of water and would bemaking a slightly faster sensitizer. You can experiment anddecide what strength is best for your own work. In anycase, this saturated dichromate solution, whether it ispotassium or ammonium, will last for a very long time

when stored in a dark air-tight bottle. Be sure to label thebottle with information regarding its contents, its per-centage, and the date it was mixed, and be sure to store itin a safe place where children cannot reach it; when mixed,dichromate solutions look a lot like sugared drinks!

X Be cautious in how you handle ammonium orpotassium dichromate: It is dangerous and poisonous.This chemical can cause lesions on your tender fleshthrough contact and can damage your lungs by breath-ing it in. Be very careful with storage and never leave thechemicals unlabeled or where children can get theirhands on them. Please reference the chemical section inthe Appendix before using dichromates.

Waterco lo rsThe watercolors you use should be of “professional” artistquality, not student or “academy” grade paint. Inferior paintoften does not clear well in the highlights and shadows andcan be one of the reasons, besides poor paper preparation,and too much sensitizer in the formula, for paper staining.There are exceptions to this warning about academy gradepaint, but I’m not sure which paints they might be. Forbeginning work it is a good idea to have “primary colors”on hand. The primary colors include red (alizarin crimson),blue (thalo or cobalt), and yellow (new gamboge or cad-mium). Naples yellow is also a nice color and is creamierthan the other yellows, as is Transparent Yellow. You mayalso wish to have a black and/or a gray such as Davy’s Gray.Of course, use any color you wish from the manufacturer’sstock as long as the quality is good. Those readers who arecolor blind, or color impaired, might be considered creative,so don’t avoid the gum bichromate process for those rea-sons. Be aware that some colors are suspect in regard to per-manence and ability to clear in the wash developmentstage. It would be numbing to provide this list because thereare so many different brands of watercolor and gouache(watercolor with white pigment added), and a color fromone manufacturer will behave quite differently than theidentical color from another. You will have to discoverthose that are best for you within the parameters you workin. I recommend Winsor–Newton, because that is thebrand I have always used. Again, keep careful notes andyou’ll work it all out eventually.

An Interesting Fact Regarding DichromatesThe speed of the emulsion will be slower in proportionto the pH of the water used in creating the coating solu-tion. The more alkaline the water, the higher its pH(above 7) and the less the dichromate’s sensitivity to UVlight. Conversely, the more acidic the water, the lowerthe pH (less than 7) and the greater the dichromate’ssensitivity to UV light.

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PaperIt is important to use a paper that is well made and able tostand up to all sorts of abuse: specifically, repeated wash-ing times of extended duration. For minimal passes, apaper with a weight of 140 lb. might be adequate. For gumprojects with several applications, exposures, and devel-opment experiences, a 300 lb. paper will work well. I haveused 1,160 lb. Arches when I have intended to make gumswhere I could use power tools and sanders as part of theworking process. In all cases, even with high-quality water-color papers, it is a good practice to gelatin size and hardenthe sizing if more than a single pass is planned for.

Gum Arab icGum arabic can come in a variety of purities. Winsor–Newton makes an expensive one that is very clear, comes

in tiny little bottles, and sells for a premium. I like the lookof their product, but it is not very cost effective. A print-maker’s supply will sell a gum arabic that is syrupy andquite dark at a price that is not nearly as precious. Don’tconcern yourself with the color of the gum, because itseems to make little difference in the quality of the print.A few gum bichromate artists claim that different types ofgum arabic have different printing speeds. They are prob-ably correct, but I’m not sure you should lose sleep overthis possibility. Gum arabic is also handy for masking.Essentially, you are buying the sap from an acacia tree, andthe color of it does not always determine the quality. Mostart supply outlets sell it by the quart or gallon to meet therequirements of printmakers and lithographers.

Using Glue as a Substitute for Gum ArabicThere is a nice idea that I have not attempted yet for usingliquid glue as a substitute for gum arabic. This formula isfrom the Randall Webb and Martin Reed book, Spirits ofSalts. First, make up a 5% potassium dichromate sensitizer(5 g to 100 ml of distilled water). Next, place a smallamount of watercolor pigment, about the size of a #2 pen-cil eraser, in a ceramic cup. Then add 5 ml liquid glue tothe cup and stir it into the paint. The Webb-Reed bookindicates that you shouldn’t be concerned if the mixture isa “rubbery mess.” Add 5 ml of the 5% potassium dichro-mate mix to the “rubbery mess,” mix the ingredientstogether, quickly coat your paper with a thin coating of thesolution, dry it thoroughly, put the coated paper and neg-ative in a printing frame, and expose in UV light. Presto!

A Trad i t iona l Gum Bichromate Sens i t i z ingFormula (Ammonium Dichromate)

9 ml gum arabic1⁄2˝ to 1˝ artist’s grade watercolor pigment

3 ml saturated ammonium dichromate sensitizer solution

Begin by adding the 9 ml of gum arabic to a small plas-tic, paper, or glass container. Next add the watercolor paintand stir the paint into the gum until it’s smooth. To sen-sitize this paste, add 3 ml of a saturated ammoniumdichromate solution and stir it into solution. Please beaware that this formula is one of those old “horses” that

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Figure 13–10Kathy Pillsbury, Gum Flower, 1998Kathy Pillsbury was another student at the Art Institute of Boston whoadopted the process of making digital negatives for her gum bichromatework.(Courtesy of the artist)

has made its way from one source to another since thebeginning of time (more or less). It works perfectly well,but it isn’t, by any means, the last word in gum formulas.Each individual will adopt his or her own personal work-ing styles, techniques, and mixes to suit his or her inten-tions and imagery. In addition, each person’s coatingtechnique, washing style, or purist to nonpurist approachwill be different according to who they are and what it isthey need from the ratios and combinations of gum,paint, and dichromate. As they say in the gum labs, “It’snot how impeccable your formula is, it’s how you use it.”

Another Sens i t i ze r Formula (Potass ium Dichromate)

This formula is generally very successful, and the pro-portions of potassium dichromate to gum are similar tothe mix used by many of the most technically successfulgum artists. Use the following ingredients and mix themaccording to the directions for ammonium dichromate.Pigments have different densities, and therefore theamounts used in an 8˝210˝ formula such as this one willfluctuate, depending on the color.

6 ml gum arabic1⁄4˝ to 1˝ watercolor pigment

6 ml saturated potassium dichromate solution

An Al te rnat ive Sens i t i z ing Formula :“The 5-10-10”This formula makes a coating that is texturally smoothand a bit pale. I like it as a formula for high detail nega-tives. It’s a good choice for print details that are delicateand built up patiently over subsequent exposures. This isa great formula for darker colors used to increase shadowdepth in gum and combination processes such as gum andcyanotype.

10 ml gum arabic (poured into a small plastic or glass container)

10 ml distilled water (add to the gum and stir)1˝ or more quality watercolor paint (add to the

gum and water and mix well)5 ml ammonium dichromate (stir into the solution to

sensitize)

Sens i t i z ing the PaperWhen your paper has been correctly sized and hardened,and you have registered your negatives with the paper sothat multiple applications of exposure are possible, it istime to coat the paper. If this is your first experience withgum, or if you have not had any success with the processbefore, select one of the dichromate formulas above andprepare for success.

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Figure 13–11Sarah Van Keuren, Phoebe Among the Leaves,1998Sarah Van Keuren teaches alternative process-es at the University of the Arts, and a number ofher former students are represented in thisbook. This is a nice example of Sarah’s combi-nation gum and cyanotype prints from an8”210” pinhole camera negative.(Courtesy of the artist)

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Select the color(s) you wish to mix for the first coat-ing. Generally, a lighter value is used first so that you canget a sense of where you will be going with the print. Thislighter color is often used to print for the highlights in thenegative. Measure a small amount of watercolor pigmentinto the gum and stir it well until it is thoroughly in solu-tion. Now add the dichromate sensitizer under low tung-sten light and stir slowly until all of the ingredients aretogether as one.

It is not uncommon to make a first exposure usingonly the gum arabic and the sensitizer. This exposure, pro-viding it is not too long, will give you a light tan-coloredimage of your negative. You may also elect to begin yourfirst gum exposure on top of another non-silver processsuch as cyanotype. In this case, your initial base color willbe blue unless you have changed it through toning.

It is quite permissible to work under normal roomlight conditions, but I generally prefer to mix my colorsunder a brighter light so I can better evaluate them. It isalso a good idea to paint a piece of the scrap paper withyour intended emulsion and blow-dry it to quickly see

what the color will look like when it’s not wet. Keep inmind that when you add the dichromate to the water-color/gum arabic solution the color will change due to theorange color of the dichromate sensitizer. Don’t worryabout this change, because the orange color will wash outduring processing.

A Few Words Regard ing Convent iona l Gum Wisdom and Sta in ingOne of the “old rules” stipulates that a greater concentra-tion of paint than “normal” (meaning more than 1˝ ofpaint in a standard mix for an 8˝210˝ print) will resultin staining in your print’s highlights. I have generallyfound that a greater concentration of paint in the emul-sion will actually result in less staining. Judy Seigel con-firms this point in Issue #2 of her excellent Post-FactoryPhotography Journal.

For many years, I have been laying multiple gum ara-bic washes on watercolor papers prior to making water-color paintings. By doing this I was able to paint and thenreturn to specific sections with a wet brush to pull awaypigment and expose highlights. This was possible becausethe paint was sitting on the gum arabic rather than thepaper. It made sense, thinking about this fact, that extrapaint would not be a significant factor in staining whensitting in a gum arabic solution. In fact, I had alwaysthought of extra pigment (more than 1˝, but not so muchthat flaking occurred) as a quasi filter, resulting in cleanervalues and less stain potential. Be aware that a greater con-centration of paint may also result in a shorter tonal scale,higher print contrast, and possible flaking.

The Relationship of Sizing Type and Color and StainingThere is a relationship between the sizing formula youselect and the final colors and highlight tonalities in theprint. A hardened gelatin sizing, which allows for the suc-cessful clearing of highlights, will occasionally hold fast tothe ammonium dichromate and stain. This results, insome cases, in a yellow tinting of color within the print.These yellowish tints can generally be cleared in a sodiummetabisulfite or potassium metabisulfite bath. Plastic siz-ing, like the gesso/matte medium formula, often providesa more “true to the tube” pigment interpretation. It does,

Figure 13–12Cheryl Harmeling, Brynmore, 1998Cheryl Harmeling, while a student at the Art Institute of Boston, created apowerful portfolio of gum bichromate portraits using a single negative andmultiple “passes” with black watercolor, ammonium dichromate, and gumarabic.(Courtesy of the artist)

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however, occasionally yield an image that results in morecontrast. There are also instances when the gesso/mattemedium will flake off in development, so keep a recordof the proportions that you are testing.

Coat ingCoating a gum bichromate emulsion on paper is not dif-ficult but requires practice. There are several ways to coatwell. One of them, the standard way, is to work on dry,sized, and hardened watercolor paper using a hake or foambrush. Mark the printing area with light pencil registrationmarks and quickly brush-coat in even vertical and thenhorizontal strokes. Work fast, smoothly, and lightly untilthe emulsion just begins to become tacky. Select the widthof your hake brush by the size of the area that you are coat-ing. Obviously, a 1˝ brush is a more difficult tool to workwith if your coating area is large. Although it is less expen-sive to use a hardware store type of foam brush, and cer-tainly viable as a coating instrument, I personally preferworking with the hake brush. This is because the hakebrush absorbs less of the emulsion, can be easily washedfor additional use, and simply feels better in my hand.Again, be careful to paint lightly, cover the entire area thatwill be printed, and to be graceful with the coating.

When the emulsion begins to “set up” (looks and feelsmore gummy than liquid), take a clean and dry 4˝ hakebrush and very gently whisk it back and forth until all ofyour application streaks have blended into a smooth coat-ing. Barely touch the paper when doing this and you willappreciate the results. Of course, if your intention is tohave a coating that is not smooth but more “painterly,”just go with your instincts and coat “gesturally” to yourheart’s content. When you are satisfied with the look ofthe coated surface, allow the sensitized paper to dry in asemidark environment or force-dry it with a hairdryer seton a cool setting because heat may fog your print—some-thing you won’t know about until you develop the image.Write down all of the technical information, such as thecoating formula, paint amounts, and type, date, time ofexposure, and stage of the print. Write this informationalso on the back of the paper for reference.

An Alternative Wet Coating TechniqueAn alternative method of coating is to first soak the pre-pared paper in room temperature water. After removing thepaper from the water bath, gently blot it until it is slightlydamp with no visible water reflection on the surface. Becareful not to abuse the paper’s fibers when blotting. Coatin the same manner as with dry paper. You may notice asmoother coating and will probably find it unnecessary touse the 4˝ hake brush for evening the emulsion coating.Dry the coated paper in a semidark environment or force-dry the print with a hairdryer set on a cool setting. It is agood idea to contact print immediately after the paper’sfresh emulsion has dried, because this will yield the bestimage. The wet coating method will give you a somewhatlighter image, which is perfectly fine because you will bebuilding your image over time with multiple applications.

Expos ing the Negat iveIt is pointless to attempt a uniform gum “standard” forexposure or contrast control, because the variables are toonumerous to define such a standard. These variables includedensity and type of pigment, humidity, time of day, nega-tive density, strength of sensitizer, type of gum arabic, typeof paper, or anything else that is a part of the process. Thereis no such thing as a “correct” exposure. As with most ele-ments of this process, each part of the process is a variablethat will change when another variable enters the equation.

The exposure is made, as in other alternative processes,with a UV light source such as the sun or UV printingunit. The advantage of a UV printing unit is that it is con-sistent year round, 24 hours a day. Gum artists workingwith a UV exposure unit are able to calibrate their workwith less guesswork, and they can better evaluate exposuretimes in a deductive manner. Other gum artists like themore organic and casual ritual of printing in the light ofthe sun. In my experience, sunlight appears to provide a“crisper” image and a faster exposure time. As with all ofthe previously defined alternative processes, you will needa hinged-back contact printing frame for sun printing.

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It might be a good idea when beginning a new printto make a test strip of exposures using a “step-wedge.” Ifyou don’t have one, lay opaque strips over the contactframe holding the negative and sensitized paper. Removea strip every 20 to 40 seconds during the exposure. Whenusing dark colors it is not a bad idea to increase the num-ber of test strips. Don’t forget to keep notes of what youare doing, including formula, time of day, and test striptimes. After making the test exposures, develop the testprint and you will have a pretty good idea what exposuretimes you should use—that day. Remember that the gumprocess is an evolving one and is more like printmakingthan traditional silver gelatin printing. Make a plan foryour printing strategies and be patient.

Pr in t ing a S ing le Co lo r Gum with a S ing le Negat iveQuite often, especially in a workshop environment thatcompresses many alternative processes within a shorttime, it is common to demonstrate the techniques ofgum with a single negative. This is a cost- and time-effi-cient method of describing how gum bichromate workswithout taking the time to produce multiple density vari-ations, like CMYK separations, of a single negative. Thismethod of demonstrating has occasionally been a sourceof confusion due to the discussion of strategy regardingprinting for highlights and shadow details within theparameters of a single source negative. The solution is notcomplicated; the key is the variability of the emulsion.

You can also play with the proportions of gum todichromate sensitizer with ratios as concentrated as 1:1or 2:1 (gum to dichromate). The reason is the contrast isbumped up by the reduced sensitivity of the emulsion andthe degree that the highlight areas will clear due to theconcentration of gum arabic in the formula. At the sametime, the open shadow areas will not completely “closeup” (overexpose) on you.

During the water development, the highlight areasclear quickly (contrast), while the exposed shadow areaswill not have had enough exposure to close up on thedetails within them. In order to penetrate the highlightdensities of your negative, make your first exposure afairly lengthy one so that the highlight details will show.You may also refer to an earlier mention of printing withonly gum and dichromate in order to lay down a “tan”-colored base for the highlight detail. This would, or could,take the place of a color if you don’t clear the paper withsodium metabisulfite or sodium bisulfite.

In a single negative/single color gum it is advisable tomake the coatings thinner and less sensitive rather thanuse a normal sensitizer mix, playing with the ratio theo-ries mentioned above. On subsequent exposures you canincrease the ratio of gum to dichromate, back to the stan-dard, adjusting your elements as you see the need. Onething to keep in mind when making a gum print from asingle negative is that you don’t necessarily want to printfor the finished image on a single pass. The reason for thisis that you may find your shadows blocking up. It’s bet-

Figure 13–13Melissa Good, Occupancy Vacancy, 1998Melissa, a former student of Sarah Van Keuren’s, created this gum bichro-mate print as part of a melancholy series of portraits in gum bichromate.(Courtesy of the artist)

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ter to parcel out exposure time over several exposures—each taking a percentage of the total time necessary tocomplete the finished density. Again, keep notes on every-thing you do.

Development : C lear ingDevelopment of the exposed gum print is very simple.There is no development chemistry, just a good watersoaking and time that may range from a few minutes tomany hours. There are ways to enhance and clear areas ofthe print that I mention in a few sentences. These are sim-ple and easy to employ during the development stage.

Following exposure, immerse your paper in a tray,larger than your paper, which is filled with ambient tem-perature water. If the water is too hot you will unwittinglyerase subtle details. If the water is too cold, the clearingwill take forever. Gently agitate the paper for about aminute and then very carefully change your water. Thenplace the print face down in the fresh water bath and leaveit alone. The unexposed areas of the image will soften anddrop gently to the bottom of the tray. If you agitateaggressively or run water on the surface of the emulsionyou will wreak havoc on a wet, fragile image. Look acrossthe paper’s surface after your highlights have cleared andyou will see a distinct bas-relief of the image. This reliefexists because the exposed (hardened) areas of the imageare still on the paper and swollen with water. The unex-posed portions of the image will be lying peacefully onthe bottom of your wash tray.

In my experience, light colors will yield a perfectlydeveloped print within 10 to 15 minutes, providing youhaven’t radically overexposed the image. Black prints willtake longer to clear than will prints with lighter colors.Single exposures with very thin colors such as Naples Yel-low or Davy’s Gray may take only minutes to clear. Clearmeans that the highlights are paper base clean and whenthe well-exposed shadow values have tonal delineation anddetail.

Often you will initially see nice separation within yourshadow details only to have them float away or drip offyour print’s surface. This indicates that you are close tohaving a correct exposure time, but those particular areassimply haven’t had enough exposure yet. Don’t throwaway the print. Wash it well, dry it, and recoat with the

same or a different color, and expose the negative againfor a slightly longer time.

Prints that have been overexposed may show less con-trast, flat highlights, or blocking in the shadows. Theseflaws can often be repaired by making a bath of 15 ml ofammonia or household bleach to a liter of water. Be care-ful because this bath is very efficient at removing a lot ofdetail in a hurry, especially if the solution is hot. This par-ticular remedy often becomes a technique, like sprayingyour cyanotypes with a mist of Tilex® toilet bowl cleanerfor an unusual reticulated effect.

Another method for clearing heavily stained or over-exposed prints is simply to let them soak for a day. Again,if you underexpose the print you only have to dry it, recoatit, register, and reprint the same color and negative. Yourexposure on this second “pass” will likely require less timeto achieve the effect you were going for in the originalexposure because you will be building on a layer of detailthat already exists. Personally, I prefer a series of smallexposures to one big exposure, but this is just a matter ofpersonal taste and workflow.

There will be times when you may not want to developthe print to completion or, conversely, when you wish toproduce an image that is significantly different from onewhere you left the print to gently soak for a total clearingof the highlights. Incomplete development, where youleave a good deal of original color behind (especially in thehighlights), can be achieved by stopping the developmentabout halfway through and laying the paper flat, face up,on a blotting surface. If you hang it to dry, the colors willrun. If you decide to abruptly stop a development inprogress because you like the way it looks, you can hardenthe image by reexposing the paper to UV light after it hasdried.

On the other hand, forced development of the print,where you wish to eliminate or transform detail, can beachieved by running water directly on specific areas of theprint. You may also change the way a print will look byusing a brush, gloved finger, or etching tool to mark inthe soft and swollen pigment. Remember, in the wet statethe emulsion is very sensitive to abrasion, and abrasion isnot always something to avoid. I have used a commercialhandheld garden sprayer, the type that allows you toadjust water stream pressure and flow size, to “draw” intothe soft emulsion. Use your imagination and have a good

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time with the options. If the end result is a mess, thenchalk it up to experience and see if you can use the knowl-edge in a positive way. The fundamental wisdom of thisis that the relationship of exposure and developmentdepends on a good marriage between the gum and thedichromate. The paint is the “unrequited suitor” and onlystays in the relationship if the gum hardens and refuses towash away.

Clearing Stains with Sodium or Potassium MetabisulfiteIn the event that you have dichromate stains in your high-lights or borders (the tan color), you may clear them outwith a simple 1% to 5% solution of sodium metabisulfiteor potassium metabisulphite. Prints can be immersed oryou may elect to spray the solution on the surface of adamp print. You might even consider selectively paintingthe metabisulfite on problem areas. You can also try potas-sium alum, but this chemical may not help the archivalintentions you have for your image. This step will be yourlast one after all of your color impressions have been made.

Clear the print in the sodium metabisulfite bath for 1to 2 minutes and wash it for 10 minutes in clean water. Becautious of the percentage concentrations of the metabisul-fites because they may be more aggressive than you hadanticipated. Be sure to do a test piece before committingyour print to a bath and adjust the percentage strength asnecessary. You may also spot-clear with this solution witha small brush. If you notice that your emulsion has becomefragile in the sodium or potassium metabisulfite clearingbaths, you may want to consider drying the print and goingto the final wash later on. If all attempts to clear your gumprint have failed you can try a few things in the next print-ing session to avoid the same problem.u First, review your sizing and hardening technique.

u Try changing the brand of paint. This can often rectifystaining in the highlights. One manufacturer’s formulafor cadmium red is seldom identical to another’s.

u In the same line of thought, try changing the type ofgum arabic you are using. There are many varieties andnot all will work exactly like another with your choiceof paint.

u Soak the print face down in a water bath—for a verylong time. This solution does have its disadvantages;

lengthy water washes will damage the paper and dete-riorate the sizing.

u If nothing is working, and you’re feeling particularlystubborn, soak the print in a solution of 1 liter of hotwater and 10 ml to 30 ml of ammonia. This solutionwill leave a lasting impression on the print, and it willlook quite different from your original intentions. Justimmerse the print and watch your image rapidly, andforever, change personality. Please be careful about thefumes that this technique brings forth.

u You can also try exposing for less time, printing imme-diately on drying, or changing paper, because differenttypes of paper will clear differently.

u Try incorporating a greater proportion of gum arabicto the dichromate in your formula. Too much sensitizermay be the problem.

u You may wish to try, after a significant degree of clear-ing frustration, blasting warm or hot water onto the printto see if you can get any separation of values and detail.Chances are you will be saying good-bye to all delicatehighlight details, but for many gum printers it is the mass,rather than the detail, that is important. Spraying warmwater can also open up blocked shadows.

u You can try using a 2% solution of Ilford’s Acid Hard-ener as a clearing bath.

u Last, but not least, you can be upbeat about the entireexperience and start over again. You might also considerusing the print as a base for another process or a can-vas for you to paint, paste, and play on.

Other Misce l laneous Troub le-Shoot ingNotes and Suggest ionsAny of these notes and suggestions may be disregarded ifthey don’t fit your working style.

First ImpressionsConsider making a cyanotype as your first color impres-sion. It provides a strong and finely detailed blue (or someother color if you tone it) and gives a fine visual map towork on. You may also consider making a gum “pass” ontop of a platinum/palladium print if you want to raisesome eyebrows. Actually, this combination was quite pop-

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ular with many Pictorialists in the early part of the cen-tury. The additional gum bichromate step helps bring outand define complex shadow details and often providesadditional depth to the image. If you intend to try this,begin with a brief green or blue gum exposure as Steiglitzdid.

StainingMany of the solutions for dichromate staining are coveredin the section you’ve just read. There is, however, also paintstaining to consider. If you are experiencing staining, tryduplicating your technique with a different brand of paint.Always use the highest quality watercolors you can buy.Student-grade watercolors often have little quality to speakof and will often end up staining your print or washingout in splotches. Some colors are particularly tough toclear, and personally I’ve always had awful problems withgreens. When I want a green I will generally mix a blueand a yellow rather than opt for the tube green. It has beensuggested that a Rowney Thalo Green clears well, but Ihave not tried it as of this writing.

You might try using a different type of gum arabic oradd more of it to the formula. You might also considerusing a different paper, trying a different sizing-hardener,remixing a fresh dichromate, using less of it in the sensi-tizer mix, or exposing your colors for multiple and shortertimes. You may also need to make a new negative with amore delineated tonal scale. Work carefully and keepdetailed notes so that you can go backwards to find theproblem.

To Darken an ImageTry repeating the same coating and negative, in registration,for a second or third exposure. You may also try a darkerpaint, a lighter version of the negative, a complementarycolor, or a little more dichromate in the formula. If you addmore dichromate to the sensitizer mix you will experiencea reduction of contrast and increase in your exposure time.Adding more pigment to your formula may or may notwork, and the success of this choice will depend on a fewother variables. Extra pigment will likely add contrast to theimage and may result in flaking of the emulsion. Keep trackof the paint amounts that you are squeezing into the gumarabic. I actually know of several very successful “gum-mists” who weigh their paint on a digital gram scale.

To Lighten an ImageTry using a lighter color, a more dilute color, or expose fora shorter time. Short exposures will often yield more con-trast because more of the pigment will unharden duringexposure and will wash out during development. Using lessdichromate in the formula will result in a solution that isslower (reduced sensitivity) and more contrasty becauseonly shadows will print out. You may lighten the entireimage by using less pigment in the formula, and this willresult in less contrast. You may also try very hot water, over-washing the exposed image, or using a solution of sodiummetabisulfite, potassium metabisulfite, or ammonia.

Figure 13–14Scott McMahon, Surveyor 1, 1997Scott is another former student of Sarah Van Keuren’s—seems to be a pat-tern here with gum bichromate—who uses himself almost exclusively as asubject.(Courtesy of the artist)

To Increase Shadow Density Without Changing HighlightsTry decreasing the exposure times of subsequent coatings.You may also try using less dichromate in the formula.Also try adding proportionately less pigment, by half, toeach subsequent formula and exposure. This allows shad-ows to build slowly and may help minimize staining in thehighlights. Many alternative gum artists will add morepigment to subsequent coatings to increase contrast. If youhave the time, try both methods and determine whichworks best for you.

To Enhance Highlights Without Blocking the ShadowsDecrease the amount of watercolor pigment you add to yoursensitizer and modestly increase the exposure time. Both ofthese options will result in less contrast in the print. You canalso achieve a full tonal range by altering the amount of pig-ment added to each additional coating, but the success ofthis tactic will be dependent on several other factors.

To Reduce ContrastUse lighter colors, use a higher concentration of dichro-mate sensitizer and decrease the amount of pigment,

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Figure 13–15Stefanie London, Tulips, 1989Stefanie, who teaches at the Art Institute ofBoston, works with many materials in the trans-lation of her intentions. This piece, made whilea student of mine at Harvard, combines gumbichromate, cyanotype, acrylic, and watercolor.(Courtesy of the artist)

expose longer, and/or develop for less time. To tone downcolors, try using their complements instead of immedi-ately reaching for a tube of black watercolor paint.

If the Highlights Will Not Print at AllTry “flashing” your entire image area without a negativein the contact printing frame with only a sensitizer coat-ing of gum arabic and dichromate and the color youwould like as a “whisper” in the highlights. You can alsosimply omit the color part of this equation and make yourhighlights a tan color.

A Single Negative StrategyIf you are brand new to this technique and have one largecontact negative to play with, here is a possible strategyfor you. Try printing a single negative with a long expo-sure and a small amount of paint. Then, for a second pass,after washing and drying the first pass, use a lot of pig-ment and a short exposure. For a third pass with the same,or third color, try using the right amount of paint, withthe right amount of exposure. You should end up withyour first good-looking gum print.

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Figure 13–16Dana Leight, 1992Dana made this compelling work as a student inSarah Van Keuren’s MFA Bookarts/Printmakingseminar at the University of the Arts inPhiladelphia in 1992.(Courtesy of the artist)

Color InventorySome gum artists like to make up their color and gumemulsions in small batches and store them in Tupperware®

or urine sample containers from the local health careprovider. This allows you to establish a color inventory andsave time. Urine sample containers are great because mosthave an embossed graduate scale on the side and a verysecure screw-cap. Next time you go in for a physical check-up, pick up a few for free. Do not add the dichromate yet.Be mindful that these solutions will not last a long timeonce the dichromate has been added to the gum andpaint mixture.

Make Color ChartsEach new paper, paint type, sensitizer, sizing, hardener,and emulsion will show you a different look. Write thisinformation on swatches, cut them into slide size shapes,and keep them in a slide sheet to use as a reference chart.

Painting on Gum EmulsionsTry painting on gum emulsions in selected areas of theprint, that is, eyes, clothing, and so on, instead of total cov-erage in the traditional manner. This allows you to addspecific areas of color without affecting the entire print.

To avoid a hard edge on the selective color, wet a fan-shaped watercolor brush in clean water and lightly dragit along the edge of the applied color before it dries. This“feathering” creates a softer edge line.

Create Area “Masks” Using GumPainting an extra coating of gum arabic in the areas youdo not want completely colored after exposure worksquite well. You can also use other masking devices in con-junction with the negative, such as rubylith film orMylar®. The image in the emulsion achieves its tonalitiesbased on the degree of its hardening. The harder it is afterexposure, the less of it washes off. The less it is hardened,the more of it washes off. Pay attention to your exposuretimes.

ExposureExposure is controlled by several factors that must bekept in mind when creating print strategy: source of light,the color of the pigment in the emulsion, the time of expo-sure, the proportion of dichromate to gum, the thicknessof the application, and the humidity. Some practitionersfind that the higher the humidity, the shorter the expo-sure. Others report the opposite is true in their work. Long

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Figure 13–17Lois Johnson,Audience FreezeInstallation, 1982The 100 figures inLois Johnson’sinstallation“Audience Freeze”at the 1980 WinterOlympics in LakePlacid, NY, weremade by screenprinting canvas withimages of gloves,scarves, and cow-boy boots. The faceswere blue gumbichromates fromortho-film negativeson Rives BFK paper.(Courtesy of theartist)

exposures will result in less contrast because more of thesensitizer becomes insoluble and refuses to clear in thewater development. Shorter exposures work in the oppo-site manner.

Photoshop and IllustratorIf you are proficient using Adobe Photoshop or Illustra-tor, try making your CMYK gum separation negatives inthe computer and having them reproduced as film nega-tives at a local service bureau or doing it yourself on yourdesktop printer. Be sure to separate in CMYK (see Chap-ter 3, “Digital Options”). In a CMYK separation set, C=thalo blue, M= magenta, Y= cadmium yellow/hansa yel-low, K = lamp black.

If Your Print’s Surface Texture …If your surface looks uneven, you can take a piece of finesandpaper or steel wool and gently give it a nice matte-luster finish by softly sanding the surface in small, circu-lar swirls.

Random Last ThoughtsTake your time learning gum printing and enjoy the sim-plicity of the process as well as its often maddening com-plexity. Unless you wish to show evidence of workingstress on the surface of your print, sometimes you just haveput the print face down in the water and do somethingelse for a while (this will make sense later on). Gumbichromate is different from others in the alternativeprocess genre, and it is unhealthy for your creative self tothink there is a perfect way to do it. I write this eventhough I know of at least six gum printers who claim thattheir technique is sublime perfection and the “only way”the process can ever be performed. The variables in gumprinting are infinite, and each individual’s intentions willnever be exactly like another’s. Play and practice are thesecrets to becoming a good gummist. Play with the myr-iad elements of gum and practice to make your personaltechnique compatible with your intentions—so that itworks for you.

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Figure 13–18Stephen Livick, Mural #528(522.4 meters gum bichromate mural)This image is another example of Stephen Livick’s artistic and technical dexterity. This Canadian artist is one of the most fearless gum bichromate artists Iknow of. Each of his mural size works takes a minimum of three months to execute.(Courtesy of the artist)