Art Business News' guide to photographic processes

Art Business News, Oct, 2003 by Susan Seiling, Laura Meyers

Over 175 years ago, Joseph Nicephore Niepce set up a camera overlooking the courtyard of his home in France. In the camera was a polished pewter plate coated with a petroleum product called bitumen of Judea. He left the lens of the camera open and, eight hours later, removed the pewter plate and washed it with lavender oil and white petroleum. An image of his courtyard remained on the pewter plate--the world's first photograph.

Since then, photography has evolved radically. New processes are constantly developed and refined as old processes are obsolesced. This glossary of photographic processes explains some of the vast and varied ways photographers translate the world into prints.

Ambrotypes

Patented in 1854, the ambrotype produces images on glass. Like the earlier daguerreotype, each image is unique, made one at a time in the camera. The glass is flowed with iodized collodion, which is then sensitized by being dipped into a bath of silver nitrate and exposed in the camera while still wet. A chemical developer is used to bring out the image. Typically, the glass plate is placed in front of black material--paint, cloth or paper--to view the image.

Bromoil Prints

A bromoil print begins as an overexposed silver gelatin print that is dried and then bleached to eliminate the metallic silver, resulting in a faint, ghostlike image. The bleached print is soaked in water; the gelatin absorbs that water in proportion to the dark and light areas. The artist then applies oil-based lithographic inks with brushes to restore the image in a painterly manner.

Calotype Negatives

William Henry Fox Talbot coined "calotype" in 1840 for his developed-paper negative, which led to the first practical method of negative-positive printing in photography. To make a calotype, uncoated sheets of writing paper are covered with a silver nitrate solution, dried and then dipped in potassium iodide to make silver iodide. Then, the paper is floated on a mixture containing silver nitrate and gallic acid. The resulting image on the negative and the positive is often diffuse. In the 1840s, calotype negatives were themselves viewed as photographs.

Carbon Prints

Developed in the mid-1800s, carbon prints have a three-dimensional texture and are able to capture a wide range of tones, creating very beautiful and distinguishable black-and-white prints.

To make a carbon print, the photographer creates a carbon emulsion, which he uses to treat a piece of tissue. When dry, the photographer contact prints the negative onto the tissue. Light hardens the darker parts of the gelatin, making the darker parts insoluble in water. When the tissue is rinsed in water, the unhardened emulsion rinses off the brighter areas of the image, and the hardened shadow areas remain. The tissue is then adhered to a final surface, such as photographic paper or gelatin-coated watercolor paper. The difference between the raised dark areas and the flattened light areas creates a three-dimensional relief on the print.

Collodion (Wet Plate) on Glass Negative

Collodion is widely used to generate negatives but is also employed to produce positives (see ambrotypes and tintypes). As a negative process, a piece of clear glass is coated with a thin layer of iodized collodion. The coated plate is bathed in a silver solution to make it light-sensitive. After this, the still-wet plate must be immediately exposed in a camera. The exposure needs to be finished before the collodion on the plate has time to dry--thus the name "wet plate."

After development and fixing, the negative can be printed on any material. In the 19th century, most wet-plate negatives were used to make prints on albumen paper, but the whites of the image generally lack the yellowish cast of albumen prints. Vintage collodion prints are difficult to distinguish from other silver prints made circa 1890 to 1910 and usually require testing by a trained conservator to identify with certainty.

Cyanotypes and Chrysotypes

In 1842, astronomer Sir John Herschel invented the chrysotype, which produces images in collodial gold, as well as the more popular cyanotype process, which results in brilliant blue images. For cyanotypes, paper is coated with an iron salts solution (rather than silver compounds) to produce a light-sensitive substrate. An object or negative is placed in contact with this paper and then printed out through exposure to sunlight, not chemicals. Washing in water fixes the image in a bright "Prussian blue" or cyan tone.

Gum Bichromate Prints

Invented in the 1850s, gum bichromate printing was popularized at the end of the 19th century by the Photo-Secessionists, who liked how the images resembled tonal watercolors and charcoal drawings. A solution of pigment, gum arabic and potassium bichromate is coated on paper and dried. Then, the paper is exposed to light in contact with a negative. Gum bichromate hardens in light, so where the negative is dark and opaque, less light hits the paper and the material doesn't harden. The gum is then washed away.