Glossary
Daguerreotype
The first practical photographic process. A copper plate coated with highly polished silver was sensitized to light with
iodine fumes to form silver iodide, which darkens very slowly upon exposure to light. After exposure in the camera, the latent
image on the plate was brought out (developed) in mercury vapor, made permanent (fixed) with hyposulfite of soda, and rinsed.
The result was a positive picture, which could not be multiplied and had to be protected by a glass cover because its surface
was fragile.
Announced by and named after the Frenchman Louis-Jacques-Mandé Daguerre (1787-1851) in 1839, the daguerreotype
has remarkably clarity. Because of the mirror-like surface of the plate, however, the picture must be viewed at a certain
angle. Daguerreotypes were produced in six sizes, ranging from whole plate (6½ x 8½ in./16.5 x 21.5 cm) through half plate (4½
x 5½ in./12 x 16 cm) to sixteenth plate (1 x 1 in./3.5 x 4.2 cm).
Developing-out paper (d.o.p.)
Papers coated with a chemical emulsion, exposed to light, and immersed in a chemical bath until the image appears, or
is "developed out." These light-sensitive papers are used in the chemical development of enlarging or contact-printing.
The predecessor to d.o.p. is albumen printing-out paper (p.o.p.).
Dry collodion negative
A variety of negatives on glass with a hygroscopic agent in the coating that will allow sufficient retention of moisture to maintain
the light sensitivity for a short period of time. One of the earliest dry collodion negatives introduced by George Shadbolt and
Farnham Maxwell Lyte in 1854 used a honey process, which was further modified by John Dillwyn Llewelyn two years later with
acidified honey (oxymel). Other processes followed using tannin, gum, sugar, tea, coffee, and various collodion combinations with
albumen, gelatin, and silver bromide. Although each variation had its supporters, and the dry collodion negatives freed the photographer from
the requirement of a nearby darkroom, these processes all lacked the superior sensitivity of the
wet collodion negative. It was only after
the introduction of the gelatin dry plate
negative that the wet collodion negative faded into obscurity.
Dye diffusion transfer process color print
A print whose emulsion material is composed of multiple layers, including a final backing layer, that together create both the
positive and the negative. The three principal layers are sensitized to the primary colors of light (red, green, and blue), with corresponding
dyes and developing agents sandwiched in between. Exposure of the print starts the chemical development process, in which the dyes
diffuse through the layers of chemicals forming the positive image on the print backing. The colors of the resulting print are unstable
and susceptible to fading. The Polaroid process, developed by Edwin Land (1909-1991) and marketed since 1948, is an example of
this technology.
Polaroid polacolor is an instantaneous photographic print, first developed in 1965. The prints have a built-in development
chemistry that requires no additional laboratory processing. Exposure and processing the film both take place within the self-contained,
sealed film "packet." Individually sensitized residual layers of blue, green, and red dyes are sandwiched in between layers of
developing agent. When the film is exposed, the developing process begins. Each light sensitive layer "records" the components of the
subject colors, and the dye developer diffuses out the negative into a receiving layer to create the positive image. Significant color loss
and shift are characteristic of this short-lived process.
Dye transfer process color print
Also referred to as dye inhibition or "wash-off" relief process. The process was originally introduced by the Jos Pé Company in
1925. The subject is photographed through filters that are dyed cyan, magenta, and yellow. The filters are then contact-printed in register on
a single sheet of light-sensitized, gelatin-coated paper to form a full-color image. The pigments of these primary colors are less
susceptible to fading and considered relatively permanent.
Duratrans
A type of transparency made by Kodak, commonly used for display purposes in advertising and trade shows.
Edition
A limited number of prints from a negative produced for commercial purposes. As in traditional printmaking processes, the
photographs are assigned serial numbers in the form of a fraction (one of twenty, 1/20, for example). The numerator denotes the position
of the print in the sequence, and the denominator the total number of prints made.
Ektacolor
See chromogenic process color print.
Exposure
The act of exposing photosensitive material to light. In a camera, exposure of film is determined by the size of the aperture and
how long it is open.
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