For monochrome work, solutions last quite a while. Factors include the
purity of your dichromate, the water used, the formulas of the tissue which
may contain soluble organic materials (sugar, etc.) and of course, the
amount of use.
As you use the same solution over and over, your tissues will be less
sensitive and will gain in contrast. You can make up for this by changing
the formulation of your pigmented emulsion. See my books on the subject.
For this reason, when doing three-color work, you should use one-shot
solutions and the colors always have to be sensitized in the same order.
Save the dichromate for less critical monochrome work.
Luis Nadeau
NADEAUL@NBNET.NB.CA
Fredericton, New Brunswick, Canada
http://www3.nbnet.nb.ca/nadeaul/