The DARKROOM COOKBOOK, Third Edition

62 THE DARKROOM COOKBOOK
IMAGE STAIN
One of the desired features of pyro/cat development is the creation of an image stain, which
adds contrast and printing density to the shadow regions and enhances areas of microcontrast.
Image stain occurs around silver grains in the emulsion and is proportional to the
amount of silver in a given area. The color of the image stain can vary from yellow-green
to brown. (General stain affects the entire negative equally, both image and negative edge; it
serves no useful purpose except to increase base � fog.)
Whereas pyro/cat-staining developers can be formulated to produce some degree of
image stain, with many the stain is minimal. However, emphasizing the stain has two benefi ts.
It fi lls in the space between the silver grains, becoming an inherent part of the image density,
and to some degree masks the fi lm grain, particularly in highlight areas. Film speed and negative
printing quality are improved. A stained pyro negative shows both acute sharpness and
reduced visible grain effect (graininess).
If the maximum degree of pyro stain is desired, use a fi xer that contains a minimal
amount or no sodium sulfi te. Sodium sulfi te is a salt, and salt inhibits image stain. However,
sodium sulfi te is used in fi xers as a preservative. Although the sulfi te can be removed from
any fi xer formula, fi xers without sulfi te will not last beyond a single day’s use. Plain Hypo is
an example of a fi xer with no sulfi te.
Enlarging and contact printing paper reacts to image stain as density. Thus the total density
of a stained pyro negative consists of the silver density plus the stain density. Because of
the color of the stain most black and white densitometers will not give an accurate reading
unless fi tted with a Wratten 47B fi lter. A color densitometer set on the blue fi lter channel will
give a more accurate reading for silver gelatin printing. If an alternative process is intended
(for example, platinum/palladium), a densitometer that reads UV would be the most accurate,
as alternative processes have most of their sensitivity in the UV range.
Second Staining Bath
It has been suggested that pyro image stain can be increased after fi xing, and before rinsing
or washing, by immersing the negative directly into the used pyro developer for two minutes
with 30 seconds of agitation every minute. The usefulness of this procedure is questionable
as it appears to create a general stain affecting only base � fog without enhancing the overall
image stain. If an alkaline fi xer is used, (Formulas: Fixers: TF-2 and TF-3) the staining bath
should not be necessary. In any event, avoid using hypo clearing agent (HCA) when using
pyro developers as the high concentration of sulfi te in them will remove the stain.
TROUBLE IN THE WOODPILE
Pyrogallol and catechol are considered to be more toxic than MQ and PQ developing agents.
However, any danger associated with either of these developing agents can be avoided by
wearing gloves when handling the solutions and mixing the powders by the submersion
method (Appendix 1: Safety in Handling Photographic Chemicals: Mixing Dry Powders).