From: Judy Seigel (jseigel@panix.com)
Date: 01/16/01-10:25:14 PM Z
Some folks may remember our scientific discussion maybe 2 months ago about
how to diagnose cause of & cure a tannish discoloration on gelatin-sized
paper. It occurred evenly all over paper sized with gelatin and hardened
with glyoxal, fairly faint, but perceptible. It was however stronger in a
drip of thicker gelatin around the edge.
Particularly peculiar was that test strips in folders prepared same way
had pristinely white paper base.
Since the stain occurred during a period of several months, I haven't yet
(nor am I especially inclined to) duplicated the effect, so that I only
had a few pieces to experiment on.
It occurred on samples of 2 gelatins: Photographer's Formulary and Knox.
In one of the samples the glyoxal was in the gelatin. In others it was
applied in separate coat after the gelatin hardened. It looked darker on
the one with glyoxal in the gelatin, but that was the Photog Formulary
gelatin, not the Knox, so I couldn't say if it was the gelatin or the
glyoxal in it.
Neither of the gelatins cleared simply from UV exposure of up to half an
hour.
Stain did clear with long (3 hour) water soak from the Knox, NOT from
the PF. I have enough left to check this distinction once more with small
swatches.
In both gelatins the stain either cleared entirely or mostly when paper
was coated with dichromated emulsion, exposed, and developed for an hour
in water with the emulsion suffused into it -- clearing even from parts of
the paper that had no emulsion coated directly on them.
That would explain why no stain seen in test strips in folder. Assumption
is that dichromate in water acted as bleach, tho am not sure Wayde
wouldn't poke some holes in *assumption,* absent more systematic proof.
Areas given UV exposure didn't clear any better or quicker in the
developing water OR the plain water....
Since this stain hasn't appeared before, I consider it fairly low on
problem list, but it was curious, as was I.
But one hypothesis about CAUSE, was wrong: Early size formulas say to add
an alkali to hardener because it helps firm up the links of the gelatin. I
couldn't do that when I switched to glyoxal, because even small amounts
turned the glyoxal brown (except bicarbonate of soda, but I decided not to
tempt fate).
SO, I theorized, the PF gelatin must be alkaline. Got the pH meter working
(don't ask!) and found it was about neutral, pH 7 something. The Knox
measured about 5.8. I suppose after soaking in tap water the pH changes
anyway, but... no help there.
One other thing: I've been going back through my gum notes in prep for
P-F #6 which will feature gum, and found several comments to effect that
glyoxal hardens BETTER for our purposes than formaldehyde. This is not to
say it does, and certainly problems of this sort, as well as keeping
working solution, have not occurred with formaldehyde (tho problems of
swooning and weeping didn't occur with glyoxal). But for instance Tom
Ferguson did a bunch of comparison tests, found the glyoxal-hardened paper
(usually? always?) resisted stain better. As did my own tests. This is
merely to reaffirm that statement about glyoxal being NO GOOD is --- now
we don't say old wives tale because that's sexist. How about unsupported
generalization?
There's also fact that I was able to harden some paper last week indoors
without killing the neighbor's goldfish & nearly ourselves in city
apartment. It may have had a stealth effect of some sort... but nothing we
noticed -- yet.
However, folks interested in INDOOR air pollution should read item about
that in the science section of today's (Tuesday) NY Times. EXTREMELY
interesting, leading me to tell them no no when they got the air freshener
out at the gym today. Of course anyway those nasty "florals" are worse
than the offense.... (Is this a digression?)
best,
Judy
This archive was generated by hypermail 2b30 : 02/05/01-11:45:22 AM Z CST