Re: dichromate stain

This discussion just illustrates how unlikely it is we'll ever arrive at
any kind of usable truth about gum printing by talking about it. It's
easy to make gum prints; the difficulty arises when someone tries to set
out a rule, or to try to explain differences in observations. These
rules and explanations almost invariably turn out to be wrong, or at
least right only for a very particular set of circumstances, so not
useful for gum printers in general.

Someone who was willing to spend years working on it and had a big
enough lab could probably make some progress, but the problem is that
there's no money for it because there's no commercial application, and
even if you were independently wealthy enough to do it on your own, or
had a university appointment and the university was willing to equip a
research lab for you without any outside funding (dream on!) and you
worked out the main effects and interactions of all the variables like
humidity, temperature, light source, type of gum, dichromate type and
concentration, paper, sizing, etc, there would no doubt still be the
odd variables that would make the final equation ungeneralizable, like
the different water in different places, if that's really a factor.

A few comments below, in spite of my qualms about making anything out of
a few anecdotes:

Judy Seigel wrote:
>

> I've used 3 lights -- BL, Daylight fluorescent, and NuArc halide and never
> noticed a difference in dichromate stain.

I've only ever used a photoflood bulb, so this information doesn't
address the question of whether my light is responsible for my lack of
dichromate stain.

>
> Another reason I have less staining is probably that my development times
> tend to be long. I gather that some folks develop a half hour or less... I
> usually develop an hour and up... and I have noticed that the really long
> soaks come out wonderfully white -- and assume that, at least in part,
> that is why I rarely if ever need a clearing bath.

Funny, Christina was just arguing yesterday that the reason she GETS
dichromate stain is because she exposes hard enough to require longer
development, and today Judy argues that she DOESN"T get dichromate stain
for the very same reason, which just shows how far we are from any
useful explanation for this.

Since I've already said that I don't get dichromate stain in my usual
practice no matter how hard I expose or how long I develop, I personally
doubt this is the reason for the difference. As I've said, my
developments are most often half an hour or less, but sometimes hours
and once in a great while a day or more, and there is no dichromate
stain regardless. I've suggested before, it's true, that I suspect
dichromate stain is a result of overexposure (or perhaps overheating as
a side effect of overexposure in the case of hot lights) but this is
with very intense lights, like 3000-watt plateburners or direct
sunlight, where I think this is an issue.

I don't know how long I'd have to overexpose with my 500-W bulb to get
dichromate stain, but way longer than anything I've ever done. Well,
actually once, when I was distracted by a noise elsewhere in the house
and went to investigate and got involved and forgot I had an exposure
going, I learned that in two hours you can get quite a lot of
dichromate stain; that print was COOKED! But I don't know the minimum
amount of exposure with my light that would create dichromate stain. My
usual exposures are 1-5 minutes; I've never had any reason to expose
longer than that.
 
>
> However, I have a hunch that the wash water is also a factor if not THE
> factor. I've heard of printers who did everything identically & one had
> dichromate staining, the other not. The only difference was geographic.
> I once brought a liter of water home from Washington State to test that...
> but a liter wasn't enough --the test got screwed up somewhow, but from the
> little I did see that was a real possibility.
>

Mmmmmmm..... well, maybe. I'm skeptical. I mean, it's not as if there's
one source of water for the whole state. Washington State water could
mean anything from the clear rivers and lakes of the Cascades to the
alkaline desert water and nuclear-waste-infected water of other parts of
the state, so what are we talking about. Determining the effect of wash
water is a research study, certainly not one I want to spend any time
on, but be my guest. But one jar of water couldn't possibly tell you
much, regardless.

 
Katharine
Received on Mon Jun 14 13:11:47 2004