U of S | Mailing List Archive | alt-photo-process-l | Re: Dark reaction of gum coating

Re: Dark reaction of gum coating

I'd say it's neither factor alone as much as together. My feeling, BTW, is that putting a coated print in a black envelope with a weight on top (no air) extends the safe period, tho I never tested that specifically.

Heheheh, I should have clarified something that Don and I have in common:

When I lived in South Carolina, just a couple hours from Don, and was rabidly gum printing for 2 years, it was the first time I ever lived in a house with air conditioning. One time Tom and I decided to just shut it off, thinking, so what if the house gets hot when we're not there. WELL, we didn't realize that HUMIDITY does the real damage. You can mold your walls and camera gear if the air conditioning is not used. In fact, while I was in grad school somehow the air conditioning was turned off in our gang grad student huge darkroom area and we came back in August to the darkroom completely molded, ceiling, walls, lenses, even the TIMER on the enlarger (metal) was covered in mold!! I was so blown away by this. The university had to come in and do one of those hepa-clean processes. We lost a bunch of stuff.

My suggestion for the black bag outside in the garage was merely to have the coated paper in high humidity and high heat (presuming plastic isn't able to hold out all moisture--no weight used, not air tight). If left in the sun, there would also be the heat factor in spades--one semester I left all sorts of plastic bags, black and seethru, taped to my outside south facing wall to test some factors with gum. I have never experienced humidity like I did in the South.

According to Kosar, if one of the factors (heat, humidity, time, air flow as Judy suggests, and as Katharine says dichromate concentration) is high that will increase DR.

In practice, I used to coat 6-9 large gum prints in my air conditioned house down there that was if I remember correctly somewhere between 35 lowest and 55% highest humidity, and that could mean wait times for the final print to hit the water to be as long as two hours if I moved right along. In room light. All prints worked fine, tho perhaps in practice I left the last one to develop longer. So my rule of thumb in South Carolina was that I did not expect the paper to last til the next day, but in MT it is not a concern I think about. I do use 15% dichromate, though (half strength am di) and down in SC I used 1/4 strength for a time til I got lazy measuring it out, and that could certainly account for some difs we all observe.

When I read that Livick and Arnow do not print in the summer months I was pretty surprised, but I bet it's that they had such a predictable workflow that when humidity came, they didn't think to adjust practice to suit it. If my summers were verboten for gum printing I'd be in deep trouble.

Now ask me how living in MT wreaks havoc with my palladium printing with such low humidity....