silver during development, forming the photographic image. Unexposed and undeveloped silver halide crystals,
still light-sensitive, remain in the emulsion.
d. The two most important components of a developer are the developing agents that are required to
convert exposed silver halide to metallic silver, and a base or basic salt to make the solution alkaline. Other
ingredients include a preservative (normally sodium sulfite) to inhibit oxidation of the developing agents.
e. The stop bath is usually a dilute solution of acetic acid. It stops the action of the developer and
prolongs the life of the acidic fixing solution.
f. The fixing agent (hypo) converts the unexposed, undeveloped silver halide crystals, which are
insoluble, into soluble silver salts that will wash out of the emulsion. The removal of these salts is necessary to
make the print permanent--if left in the emulsion, they will darken in light.
g. With conventional fiber-base papers, the solutions penetrate the paper base. Complex silver salts
formed in the fixer saturate the paper at the end of the fixing step. These must be removed both from the
emulsion and from the paper base to prevent staining and fading of the image.
h. A wash of at least an hour in continually changing water at 20,C (68,F) is required for complete
removal of these dissolved salts from single-weight base. A longer time is required for double-weight paper. The
time required to wash the salts out of the emulsion alone is relatively short, about 4 minutes. Most of the long
wash time is required to remove them from the base paper. The total time usually required for a conventional
process up to the drying stage is about 1 hour and 15 minutes.*
i. Drying prints on conventional papers can be accomplished in a number of ways. Air-drying of prints
may take hours; this time can be shortened by blowing warm air over the drying prints.
j. Heated drums with canvas belts are used to speed up the drying process to a time of several minutes.
Lustre and matte-surface papers are dried with the emulsion surface away from the drum. In order to attain a high
gloss on conventional papers, the emulsion is ferrotyped against the smooth, polished surface of the drum.
k. Ferrotyping requires constant vigilance. The surface of the drum must be kept free of scratches, since
such marks result in scratches in the ferrotyped surface of the prints. Also, the drum surface must be kept clean
and polished so that prints do not stick to it.
Water-Resistant Papers: Water-resistant papers are made by coating the paper base on both sides with a
resin layer. The coating on the emulsion side, which replaces the baryta coating on conventional papers, is
pigmented white, or the same color as the paper tint. The pigmenting is unnecessary on the base side. Water does
not penetrate the resin coating, and thus the