report on glyoxal yellowing

Hi all,
     It has been a month since I sized the glyoxal test pieces. I was
actually surprised by the results. Mind you, one tester does not a science
make, but I have yellowing after a month and I can tell some things.
     I tried both the 25 ml mixed into the hot gelatin and the separate
glyoxal bath after the paper had been coated and dried with the gelatin.
All papers were Fabriano Artistico cold, hot, soft. I have sheets of glut
sized paper hardened at the same time for comparison sake, and paper not
sized, but soaked once.
     Results: air freely circulating vs air not circulating; no difference.
Room light vs. dark photo bag vs dark cupboard, no difference. The test
samples outside were a bit paler in yellowing, but I cannot discount
bleaching of the hot direct sun in a month's time.
     All samples showed consistent yellowing, and the yellowing was the
worst in the hot press and cold press for all sampled conditions (air plus
room light, air plus room dark, air plus sun light, no air plus room light,
no air plus no light, no air plus sun light). Soft press yellowed also but
not as badly. Cold and hot would be termed cream colored papers, or ecru,
now.
     I can deduce (I think) that paper type is a factor. It makes no sense
that the bumps would be the factor, since cold is bumpy, hot is not and soft
press is in the middle yet the whitest, so the papers must have something in
them different. My feeling that the alkalinity of the paper is the factor
of whether the glyoxal yellows or not is probably something I should test.
I have felt this way since Judy mentioned that baking soda added to the
glyoxal solution turned it bright orange (if I remember correctly). Since
it was consistent across the board that all test samples showed more
yellowing in the cold and hot and not soft, it would be interesting to know
if the pH of those two papers was higher, or some other sizing ingredient
was different.
     I did not test the rinsing out of the glyoxal as Judy does, which may
alleviate all yellowing, or maybe not. I guess I would say that glyoxal is
not a suitable hardener for some papers.
      As far as time factor, I noticed a bright orange bead of gelatin on
the edges of my paper within several weeks. I'll see if it disappears in
doing my gums.
     That's all she wrote,
Chris
Received on Wed Nov 10 20:39:07 2004