U of S | Mailing List Archive | alt-photo-process-l | RE: Gum Humidity Question

RE: Gum Humidity Question

Judy asks:

"1. Would you explain the function of the damp-dry-damp cycle?  I take it
this is for multiple-coat gum. So that gets it to the same size each time,
in a way just one dampening wouldn't? Do you "explain" this, or simply
appreciate it?"

My prints are rather large, so for the purposes of even coating and for
registration they need to be damp and swollen.  I dry them quickly for
quicker turnaround time.  Sometimes the print expands too much, at which
time I hit is with a hairdryer until all my registration marks line up,
place a piece of glass over it, and put it under the light source.

"2. Do you also preshrink ?"


"3. I was surprised to read those very long times for the spontaneous
whatever you want to call it graph discussed earlier.  My own finding has
been that keeping coated paper more than a few hours before exposure &
development at even "normal" humidity is likely to cause
development/stain/D-max "anomalies."  I take it from your comment that
you've found keeping problematic as well, so 24 hours wait without "ill
effects" is noteworthy...?"

Actually, when I said I kept it for a day, I meant a "work day".  In
practice I seldom keep coated paper longer than eight hours, and yes, it
does start to have ill effects.  I have used paper that has been kept
overnight, though.  While it is still useful, it might need a little
"persuasion" to clear:  brushing, spraying, etc.  But I would have to say
that I see no anomalies with paper that has been kept for 6 hours.

"4. You don't get emulsion clinging to negative when exposing "quite damp"?"

It sometimes happens.  I use lith negs.  When the negative clings to the
print (keep in mind: it hasn't dried because it has only been under glass
for 4-6 minutes) I usually rinse it in water. A hassle, but it prevents the
dichromate from bleaching the negative.

"PS.  I did some tests years ago with additions of ammonia to the gum
emulsion, then exposing after a day or even two days.  Some of the effects
were in fact interesting, but ultimately I decided more trouble than worth
for whatever they were."

Can you describe the nature of these effects?  How much ammonia did you add?

And PPS: I've not found glitches in gum emulsions on gelatin with 1 drop
Kremer anti-foam per liter as Ryuji claims he has. In fact the coat seems
about as easy & good natured as gum coating gets. That may be due to the
other ingredients involved, mine being different from his -- or simply
personal talent (or both).