photographic processes

John Murray (Scottish, 1809–1898; active in India, 1833–1871),
Taj Mahal from the East with Dr. John Murray Seated in the Foreground, 1858-62. Clark Art Institute, 1999.35.1

Albumen print: The most common photographic process used during the second half of the nineteenth century, the albumen print is characterized by its glossy surface. In this process, a sheet of paper is coated in a combination of ammonium or sodium chloride and fermented egg white (albumen). After coating, the paper is immersed in a bath of silver nitrate, which makes it sensitive to light. The sheet is then placed in a frame with a glass or paper negative and exposed to light. Following exposure, the paper is washed, the image is fixed with a sodium solution, and finally the print is dried.

Collotype: Among the first photomechanical processes to be widely used, the collotype was popular from the 1850s until the 1890s, when the halftone (see below) became more efficient and economical. A collotype is printed from a plate upon which the image from a photographic negative has been transferred. To transfer the image, the plate is first coated with a light-sensitive gelatin layer. Once the gelatin dries, the plate is put in contact with a negative and exposed to light. The gelatin hardens selectively, causing the darker areas to sit higher on the plate and the lighter areas lower. The plate, now holding the transferred image, is inked and printed. The varied surface accepts different degrees of ink, which creates tone.

Cyanotype: The cyanotype is a camera-less photograph. The photographer first coats paper with a chemical mixture, making it light sensitive. Next, an object (such as a leaf) or a negative is placed directly on the paper and exposed to light. The chemical mixtures on the paper create what is known as ferric ferrocyanide, from which the cyanotype gets its name. When the print dries, it turns blue.

Daguerreotype: Among the first photographic processes, the daguerreotype was invented by Louis-Jacques-Mandé Daguerre and debuted in 1839. The process begins by exposing a polished copper plate to heated vapors of iodine, which leave a thin layer of silver salts on its surface. The plate is then placed in a camera, exposed to light, and treated with fumes of heated mercury. To complete the process, the image is fixed with iodine and washed. Daguerreotypes have a highly detailed, mirror-like surface and often require physical manipulation by hand to view.

Gelatin silver print: The commercial development of the gelatin silver print in the 1880s revolutionized the medium of photography and ushered in the age of the amateur photographer. The process requires specially prepared paper that has been coated with a solution of silver salts in gelatin. Such paper could be machine-made, omitting the need for a photographer to create emulsions to sensitize paper. When exposed to light with a negative, the treated paper produces an image. After exposure, the paper is submerged in developing solution and fixed.

Gum dichromate: Developed in 1895, gum dichromate prints are made by applying dichromate salts to a regular sheet of drawing paper. The paper is then coated with a mixture of gum arabic and pigment and contact printed with a negative. Once the sheet of paper is washed, the gum softens, allowing the artist to manipulate the surface of the print before it dries. This technology produced images closer in appearance to traditional graphic techniques than to conventional photographs; it allowed artists to manipulate tones and details, producing atmospheric effects.

Halftone: Halftone is a photomechanical printing technique whereby a photographic image is transferred onto a metal plate as a pattern of dots of different sizes. The plate is then sensitized with a coating and relief printed. The dots that make up a halftone visually simulate the continuous tonality of a photograph. Halftone images were most commonly produced to illustrate books or newspapers.

Paper negative: To create a paper negative that can be printed, a sheet of ordinary writing paper is coated with silver nitrate and then treated with a series of chemical solutions to make it photosensitive. The sheet is then exposed, washed, and developed, and the image fixed. Photographers often waxed their negatives to speed the exposure process and increase transparency.

Photogravure: Between the 1880s and 1910s, photogravure was used as both an artistic process by printmakers and as an illustrative process for books. Over the past two decades, photogravure has been revived as a creative process. A photogravure is made by transferring a photographic image onto a metal plate (usually copper). The plate is first coated with a light-sensitive gelatin tissue paper, which has previously been exposed to a photographic positive. The plate is then etched with acid.

Platinum print: Platinum prints are known for their rich tonal range. A sheet of paper is sensitized with a solution of iron and platinum salts, exposed through a negative, and then chemically developed. The image is made up of black or brown platinum metal that is embedded in the uppermost paper fibers, resulting in a velvety, matte appearance.

Salt print: To create a salt print, a sheet of paper is first coated with salt and silver nitrate, which makes it photosensitive. The sheet is then placed in contact with a negative and exposed to light. Finally, the sheet is washed, fixed, and dried. Salt prints are characterized by their hazy, soft tonality.

Woodburytype: A woodburytype is a photomechanical process that creates a continuous tone similar to halftone or photogravure (see above). First, a gelatin film is exposed to a photographic negative. The gelatin hardens in relation to the amount of light that passes through the negative. The gelatin is developed in water and pressed into a metal plate so that it can be printed.

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