Chapter 1: Processes – LINGUA FRANCA – A Common Language for Conservators of Photographic Materials

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Chapter 1: Processes. Image of a man standing beside a seated woman. Behind is a waterfall.

Processes

Daguerreotype

Dates of major use: 1840-1865

Inventor: Louis Jacques Mandé Daguerre (1839)

A daguerreotype is an image formed on a copper plate coated with a thin layer of silver, which can appear to be a positive or a negative depending on the angle it is viewed. They were often hand-coloured. Because the silver-coated plates of daguerreotypes were extremely fragile, they were always protected under glass.

A hand-tinted daguerreotype portrait of a seated man holding a hammer.

Salt print

Dates of major use: 1840-1860s

Inventor: William Henry Fox Talbot (1839)

A salted paper photograph is a positive printed from a negative on a chloride and silver nitrate photosensitized paper support. To produce the image, a negative is placed in contact with the paper. Following exposure to light, an image appears and must then be fixed. By using ordinary paper, prints have a matte surface and warm image tones, from deep red to purple, which is achieved depending on the sizing of the paper. Characteristics are visible paper fibres and fading.

Three shelves with various different glasses and crystals.

Albumen

Dates of major use: 1850-1895

Inventor: Louis Désiré Blanquart-Évrard (1850)

An albumen is a positive photograph on a paper support. The silver particles are suspended within the albumen layer, which is made of egg whites and sensitized with silver nitrate. The sensitized paper is placed in contact with a negative and exposed to light, which results in a contact print by printingout. The final processing steps are fixing and washing. Gold toning was introduced at a later date. The image tones range in colour from brown to purple to bluish black, depending on the processing. Characteristics include some visible paper fibres as well as overall small cracks and fading into an overall yellow discolouration.

Three young girls huddled together, in front of a building.

Ambrotype

Dates of major use: 1855-1865

Inventor: Scott Archer (1852), J. Ambrose Cutting (1854)

An ambrotype is a collodion emulsion on a glass support. This negative on glass is underexposed and treated with a chemical solution that results in a silver image with a whitish tone rather than a brown tone.

To make the ambrotype a positive, a dark material such as paper, velvet or applied lacquer is placed against the back. These images are also housed in cases similar to those used for daguerreotypes and tintypes.

Two women standing, holding each other, while crying.

Tintype

Dates of major use: 1855-1860s

Inventor: Adolphe-Alexandre Martin (1853), Hamilton A. Smith (1856)

A tintype is a monochromatic direct positive image that is formed on a thin metal plate covered with a black varnish. They were often hand-coloured. Tintypes can be presented in paper mounts to be slid into albums or protected in American cases under glass.

Lantern slide

Dates of major use: 1850-1950

Inventor: Christian Huygens (1629-1695), Langenheim Bros (1850)

A lantern slide is a transparency of a positive photograph on glass. It is viewed either by projection or by transmitted light. These images can be made using albumen, collodion or gelatin. To view lantern slides, a magic lantern was used.

Three racing women at the finish line.

Collodion negative

Dates of major use: 1851-1890

Inventor: Frederick Scott Archer (1851)

A collodion negative is a negative made on glass. It is coated with cellulose nitrate, which makes it sensitive to light. The emulsion may be uneven or absent along the edges. This may result in a non-image area. It may also be missing varnish along the corners if it was coated unevenly, which could lead to areas of silver mirroring. The glass itself could also be hand cut, and thus have uneven edges. Overall, the tones are warm, ranging from creamy white to light and dark beige.

A negative with transmitted light of three costumed children, one seated on the left and the other two standing.

Carbon print

Dates of major use: 1870s-1900s

Inventor: Louis-Alphonse Poitevin (1855)

Carbon printing, called the "unalterable powder process" at the time, is a non-silver photographic process invented by Louis-Alphonse Poitevin in 1855. Its principle is based on the action of potassium bichromate, which hardens gelatin after exposure to light. A sheet of paper is coated with a mix of bichromated gelatin and pigment. It is then exposed to light in contact with a negative. The image is obtained in warm water. Areas exposed to light are hardened and become insoluble, while, in areas that have not been exposed, the gelatin and the pigments dissolve in the water. The invention of the "carbon transfer" in 1860 helped improve the rendering of mid-tones. The image layer is removed from its original support before being transferred to a second support. To tackle the problem of the image being reversed during a single transfer, photographers then developed the double transfer technique, which allowed them to reproduce the true orientation of the image.

Man with a beard and a hat with a large rim, half seated, leaning on a chair arm.

Platinum/Palladium

Dates of major use: 1880 -1930s

Inventor: William Willis (1873)

A platinum (or palladium) print is a photograph on an uncoated paper support. The paper is sensitized with a solution of potassium chloroplatinate and ferric oxalate. Exposed in contact with the negative, the sensitized paper is then developed in potassium oxalate and immersed in a series of hydrochloric or citric acid baths, and finally washed in water. Characteristically, these images have a wide range of mid-tone density values ranging from black to pale grey.

Two young girls both looking away from the camera in a dark room.

Cellulose nitrate negative

Dates of major use: 1888-1951

Inventor: Hannibal Goodwin (1887), George Eastman (1889)

Cellulose nitrate was the first transparent flexible plasticized base that was commercially available. A major drawback is that it decomposes over time and transforms into brittle shards. It is extremely flammable and therefore dangerous to store in a photographic collection.

There are three ways to identify nitrate film-based negatives: by inspecting edge printing and notch codes for dating information, by testing the materials (polarization, diphenylamine test, burn test, float test) and by looking for nitrate film deterioration.

This nitrate negative bears an inscription: No. 7 Draft, "C" Battery, R.C.H.A. It is dated between 1914-1918, which falls within the 1888-1951 date range for the use of nitrate film.

A negative of a group of soldiers, seated and standing, in front of a dog with nine legs and a very long body.

Autochrome plate

Dates of major use: 1907-1935

Inventor: Auguste and Louis Lumière (1903)

The autochrome plate patented in 1904 by the Lumière brothers was designed to be viewed using handheld devices or displayed using carbon arc lamps. It was made with miniscule grains of potato starch dyed red-orange, green and blue-violet on a glass plate. Lampblack was added to fill in the gaps between the grains. It was then laminated and pressed. A black-and-white gelatin emulsion was added as the lightsensitive layer. The small particles of colour can be noticed while viewing.

Woman wearing a long orange coat, a red hat and a long white skirt, beside a large pink flowering tree.

Cellulose acetate negative

Dates of major use: 1925-1950

Inventor: Film manufacturers

Cellulose acetate film was used as a safe replacement for the unstable and highly flammable cellulose nitrate film.

There are three methods to identify negatives: by inspecting edge printing and notch codes for dating information, by looking for acetate film-based deterioration and by testing the materials.

The edge printing on this negative is obvious, as the word "safety KODAK" is labeled on the emulsion side of the upper right edge of the negative border. There are also two V- and two U-shaped notch codes, which correspond to Kodak 14B safety negative sheet film.

As for dating the material, cellulose diacetate sheet film was used from 1925-1950 and cellulose acetate propionate was in production from 1930-1945. We also know the provenance of this negative of Sir Winston Churchill, which was taken by Yousuf Karsh on December 1941.

Therefore, we can accurately say that this negative is made with cellulose acetate.

Close-up of a corner of a negative with the word 'SAFETY KODAK', beside two V- and two U-shaped notches. A negative of an elderly man standing, with one hand on his hips and the other atop a chair.

Chromogenic print

Dates of major use: 1960s-1990s

Inventor: Rudolph Fisher (1935)

The chromogenic print, introduced in the 1940s, is a silver-based photograph. The colours are formed by chemical synthesis during development. Traditionally a chromogenic print was produced using film in an enlarger. The enlarger projects light through the negative onto the photographic paper. With the advent of digital photography, a chromogenic print could be produced from a digital file using lasers or LED lights that project the image onto the photographic paper. The processes are similar as the photographic paper is processed using traditional chemicals.

A colour photograph of an interior view of a staircase.

Credit: Rodolphe Hammadi

Dye destruction print

Dates of major use: 1963-present

Inventor: Bela Gaspar (1930), CIBA (1963)

Marketed starting in the early 1960s under the name Cilchrome®, then Cibachrome® and finally Ilfochrome®, dye destruction print is a silver process colour print obtained using a positive transparency. An image is formed from the selected bleaching of dyes (subtractive three-colour synthesis). The print support is composed of gelatin layers of yellow, magenta and cyan on laminated paper or pigmented plastic film. The dyes are destroyed according to the amount of light received when exposed during development. The technique gradually disappeared after the 2013 bankruptcy of Ilford.

Two little girls standing on a dirt road. One is wearing a yellow coat, while the other is wearing a blue coat and holding a white scarf.

Credit: Loretta Lux

Dye diffusion print

Dates of major use:1948-2008

Inventor: Edwin H. Land (1937), Impossible Project 2008- currently

Dye diffusion prints were introduced in 1948 with the invention of the first Polaroid® device by Edwin H. Land. An integral film consisting of a receiving layer and a negative is loaded into the device. Immediately after the shot is taken, the film is manually removed or ejected from the device, a pod breaks open between two rollers releasing the reagent, which spreads between the negative and the receiving layer. The image is formed using a transfer/diffusion process. For black-and-white films, unexposed photosensitive salts are transferred from the negative to the positive. For colour Polaroid® films, introduced in 1963, dyes are transferred from one layer to another. A final chemical reaction fixes the image.

Link to Atelier de Restauration et de Conservation des Photographies de la Ville de Paris website

Boy in a jean jacket and a black t-shirt with writing.

Credit: Anne Cartier-Bresson

Back of a photograph with text and numbers on the white trim at the bottom.
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