Developing and printing pictures

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Say cheese:Redox in photography

We have taken lots of pictures in our life.

But do you know about the knowledge of photography?

Now,

Let’s study about Let’s study about Redox of Photography.Redox of Photography.

Say Cheese!Say Cheese!

Understanding natural redox reactions such as the one that occurs in sulfur volc-anoes has allowed chemists to develop many processes that make use of oxidati-on and reduction reactions. Without them, photographs wouldn’t exist.

Leonardo da Vinci

described a primitive ‘camera’ before 1915

In which someone had to trace images focused on a glass plat inside a box. He was an Renaissance polymath: painter, sculptor, architect, musician, scientist, mathematician, engineer, inventor, anatomist, geologist, cartographer, botanist, and writer whose genius, perhaps more than that of any other figure, epitomized the Renaissance humanist ideal.

You must know this picture….

L.J.M DaguerreL.J.M Daguerre

--Fixed the image in a camera on highly polish, silver-plated copper to make the first photograph in 1838.In 1826, prior to his association with Daguerre, Niépce used a coating of bitumen to make the first permanent camera photograph. The bitumen was hardened where it was exposed to light and the unhardened portion was then removed with a solvent. A camera exposure lasting for hours or days was required. Niépce and Daguerre later refined this process, but unacceptably long exposures were still needed.

For the process which was eventually named the Daguerreotype, he exposed a thin silver-plated copper sheet to the vapor given off by iodine crystals, producing a coating of light-sensitive silver iodide on the surface. The plate was then exposed in the camera. Initially, this process, too, required a very long exposure to produce a distinct image, but Daguerre made the crucial discovery that an invisibly faint "latent" image created by a much shorter exposure could be chemically "developed" into a visible image. The latent image on a Daguerreotype plate was developed by subjecting it to the vapor given off by mercury heated to 75° Celsius. The resulting visible image was then "fixed" (made insensitive to further exposure to light) by removing the unaffected silver iodide with concentrated and heated salt water. Later, a solution of the more effective "hypo" (hyposulphite of soda, now known assodium thiosulfate) was used instead.

Early photosEarly photos

Early photos were called: daguerreotype

In a daguerreotype, a redox reaction between silver and iodine fumes produced a layer of the polished photografic plate.

Exposure to light caused decomposition of the silver, which was then treated with the fumes of heated mercury to form bright amalgam areas.

Modern photographic film is made of a plastic backing covered with a layer of gelat-in, in which millions of grains of silver bro-mide are embedded. When light strikes a gr-ain, silver and bromide ions are converted into their elemental forms through a redox reaction.

The equation for this redox reaction :

2Ag+ + 2Br-→ 2Ag + Br2

1. At first, the organic compound hydroquinone is usually used for using a solution of a reducing agent, or developer. The developer reduces all the silver atoms in any gain of silver bromide that was hit by light, but it doesn’t react with silver ions in grains that were not exposed to light, an image having light and dark areas is produced.

2. A solution of a fixer containing thiosulfate is added. Thiosulfate ions react with unreduced silver ions to form a soluble complex, which is washed away. This prevents unreduced silver ions from becoming reduced and darkening slowly over time.

AgBr+2S2O32-→ 【 Ag(S2O3)2 】 3-+Br-

3. Remove any remaining developer or fixer solution. The photographic nagetiv-e is reverse of the image photographed; in a word, light areas in the scene are dark on the film, and vice versa.

4. When light is shone through the negative onto light-sensitive photographic paper, a photographic print is made. The print is positive; light and dark areas are identcal to those in the scene.