From: J. Wayde Allen (wallen@lug.boulder.co.us)
Date: 11/08/00-11:52:10 AM Z
On Tue, 7 Nov 2000, Judy Seigel wrote:
> Let's say I want to find out why the gelatined paper hardened with
> glyoxal that sat on the table, but UNDER some other paper, for 6
> months discolored, and my test strips in the file are as white as the
> driven snow.
>
> My theory now is that something in the applied dichromate (if the print is
> made promptly, as the test strips were) forestalls the discoloration.
> That it wasn't *where* the papers were stored, but what stage they were in
> that made the difference.
OK, let's start trying to figure out what you really want to know? From
what you've written I get:
1. What is causing the test strips to yellow?
2. Does dichromate affect the staining?
3. Does the storage location have anything to do with the staining?
> To test, I would put the same paper side by side
> on the table, one with a test strip exposed & developed on it, one blank.
I'm assuming that your exposed and developed test strip is paper that has
been sized, hardened with Glyoxal, coated with the gum emulsion, exposed
for some length of time, and then water developed? Are you exposing
through a step tablet? What do you mean by blank? I'm guessing this is a
piece of the same paper that is sized and hardened with Glyoxal - correct?
At any rate, what can you learn from either a positive
or negative result? With your test, if one of the tests stain, but not
the other, can you answer the question you set out to answer? I would
submit that you really can't answer either question 1 or 3 that I listed
above. You do get some indication about question 2, but it is hard to say
that it was simply the dichromate that caused the effect. Could the
exposure have also played a role in the staining? What about the water
development?
One particularly odd thing is that you are simply ignoring environmental
conditions. If these have any bearing on the staining you get no
information about it. This is one of the reasons why your tests may not
give the same results in someone else's lab.
Also you say that the strip that were under some paper on your desk
yellowed whereas those in your file didn't. Any reason why you discounted
the possibility that something in the paper laying on the test strips
didn't contribute to the staining?
> One variable, right?
No, and what's worse you really haven't indicated what your supposed one
variable is? What I'm counting off hand are:
Paper substrate
strips covered by paper or not
Type or brand of gelatin sizing
Pigment type or brand if any
dichromate type (ammonium or potassium?)
exposure
development water (distilled or tap?)
environment (lots of variables - illumination, temperature, etc.)
I'm sure we can look at this longer an come up with more, but the point is
that your simple test isn't really that simple. I'd guess that you are
using the same paper type for all strips, that everything is sized with
the same gelatin, that you've only chosen one dichromate, and that you
only are using one pigment if any at all? You would be correct to say
that these variables are controlled. Of course, by locking these down, you
get no information about what affects they may have on the staining. You
have also seemingly ignored several possibly key variables:
other paper in contact with strips
development water
exposure
environment
You can only do that if you can make the case that they are not important
to the staining process. If these do matter, then you've got a problem.
That is what I understand about your test. You'll have to correct any of
my mistakes and misunderstandings before we can look at this much deeper.
- Wayde
(wallen@lug.boulder.co.us)
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