Staining seems to be a property of the amount of exposure and the clarity of
the gum in addition to the amount of wash time. For a long time I used
Tri-Ess gum for the darker tones and Photographers Formulary gum for the
light tones or pastel colors. Lately the gum from Formulary seems to be
darker so I found myself washing (soaking) longer.
I discovered the degree that staining changes the quality of a print by
accident, after overexposing a print that didn't clear in a normal amount of
time ( a couple of hours) I decided to leave the print floating face down in
a tray overnight. The next day when I lifted the print I found a beautiful
print with an ugly brownish circular patch in the middle where an air bubble
had formed. A few quick tests without adding pigment seemed to suggest that
the print needed to soak at least 8 hours to remove most of the stain and
prints left soaking for up to 24 hours seem much improved beyond that.
My next test concerned multiple coats, as this is what most of my prints are.
I found that a print coated, exposed and washed for two hours, dried,
recocated and reexposed then washed (soaked) for 12 hours had very little
staining difference from my single coat washed 12 hours. This suggested to
me that the stain will continue to clear even though covered by another coat.
Given this I started printing my gums by exposing for the highlights first.
And even though the color and density of the first coats are too dark and
muddy with each subsequent wash they will lighten. As the last coat is the
"shadow" coat usually black a little staining doesn't seem to hurt at all.
As I often know when starting that a print will be a least 8 to 10 coats I
very seldom wash a properly exposed print beyond 2 hours for the first few
coats.
Bernard Boudreau