Re: Dark reaction of gum coating
Yes--when I kept gum papers around for several days. Actually, I could get by in dry MT that is 15% to 30% humidity (winter/spring) with up to 6 days before exposure (not that that was a good thing), but MN in the summer with 80% humidity was no good for keeping paper any length of time. How you can test it (very easy!) is take a coated piece of paper, put in a light tight photo black bag, and just leave it in your humid garage in the dark for several days. Then expose your gum print and see what you get--usually a verrrrry flat image where the highlights don't clear much. Humidity, heat, and time are all three responsible for the acceleration of this.
Back in the day they used to use continuing action to expose their prints! They would expose for part time, then leave it sit for some days, then develop, to get the layer to "stick" better. But of course this is different than what you are talking about with dark reaction where no light occurs.
I actually had a day in MT this summer where the humidity was as high as 50% in the house!! But usually we are semi-arid.
----- Original Message ----- From: "Don Bryant" <firstname.lastname@example.org>
Sent: Thursday, August 02, 2007 10:49 AM
Subject: Dark reaction of gum coating
Hi Listers, I'm curious if anyone who prints with gum emulsions can say if they have actually encountered dark reaction. And if so under what circumstances did that occur? Thanks, Don Bryant