Re: dichromate stain

Dave Soemarko wrote:
>

>
> The effect of dark hardening is that the gum is hardened everywhere and at
> every thickness rather than proportional to exposure. If the paper is
> allowed to dark hardened just right (before it causes fog), then the effect
> is that you have a slightly longer scale (because in effect you are using a
> harder gum so the highligh won't wash out as quickly). I believe this is
> part of the reason some literature says that some people like to use the
> paper the next day after coating. Knowing this effect, however, I found that
> I can achieve the same thing by preflashing (after test strip and calculate
> the right amount of flashing just like one would calculate the preflashing
> for paper or negative).
>
> Dave S

Well, the dark reaction is extremely variable. Referring back to the
dark reaction test I posted the other day

http://www.pacifier.com/~kthayer/html/Current4.html

I sure wouldn't want to try to print over that, even after only five
hours. So I think the flashing strategy is probably better as a way of
putting down a slight tone than relying on a dark reaction that can run
the gamut from extreme, like mine, to nonexistent. Remember there are
scientists who say they cannot produce a dark reaction, cannot find the
least bit of Cr(III) in the film even after a week) unless they
introduce sulfide ions or other contaminants into the mix, so maybe my
gum is dirty and Keith's is clean, or something. But on the other hand
if that's it, you'd think that people who print with that dark gum
that's full of dirt and twigs and stuff would get dichromate stain all
the time. This is giving me a headache, I'm going to follow Keith's
example and go print gum.
Katharine
Received on Wed Jun 16 09:40:49 2004