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

RE: Dark reaction of gum coating

Don, I haven't measured this, it's just a feeling I've gotten -- but I think there's a sudden point where the effect cuts in. My studio right now is 63 % relative humidity and 83 degrees F, and I had the air conditioner on last night and the doors closed today (I was downstairs on the computer) so the humidity remained that "low." Still, with these measures, I would expect distinct dichromate stain, even with prompt exposure.

Sometimes the visual effect of that stain, btw, can be stunning, and I tried several times to replicate it with paint, though I failed, dismally.

Meanwhile, I sat outside on the front stoop this evening with daughter & her friend for about an hour, the humidity was higher than indoors, probably about 70%, also the temperature, and there was absolutely no breeze. The sun was down but we were sweltering. Then the police tow truck arrived and decided to tow daughter's friend's car, which as it happened was double parked... somehow the friend talked him out of it, but he was quite nasty nevertheless. That tow comes to about $300 including the fine, so I think they didn't appreciate the escape sufficiently.

They say it's not the heat it's the humidity but I think it's (what do you call it? the product?) the one multiplied by the other.

Meanwhile, 75 degrees Fahrenheit sounds quite temperate, from New York in August... But a breeze makes a helluva difference.

But Don -- maybe the difference is the digital negatives?


On Thu, 2 Aug 2007, Don Bryant wrote:

Thanks to everyone that commented about DR.

A couple of weeks ago I coated two sheets with the same
pigment-gum-dichromate mixture and deliberately placed them inside a metal
cabinet and left them over night. So about 12 hours later I coated two fresh
sheets the same way and then exposed all 4 sheets with a step tablet within
a 20 minute period. I got virtually identical results with all 4 step
tablets. The RH was over 60 and temp was about 75F during the whole period
of dark storage. I was a bit surprised that prints showed no effect of DR.

So I'm not denying DR occurs, I just haven't seen it. Thus I just don't see
how coating a few sheets together in a batch and exposing and processing
within an hour or so can make much difference regardless of the
environmental conditions, which is what I do frequently. And I don't
consider my coating and processing technique to be sloppy as I aim for
consistency since I'm printing with digital negatives.

I suppose everyone's mileage varies as they say,