Judy Seigel (jseigel@panix.com)
Wed, 13 Jan 1999 16:54:51 -0500 (EST)
On Wed, 13 Jan 1999, Henk Thijs wrote:
> Last year August I prepared some gum arabic in the usual way : arabic gum
> powder with distilled water, a one night stand and then a few drops of
> formaldehyde as finishing touch. First prints were okay, but after some weeks
> -I cannot exactly point out how many - nothing worked anymore. Pigment
> clearing of the print was nearly impossible; less exposure, less pigment,
> forced development....it was a frustrating exercise, nothing compared to the
> halleluia after the first prints. The only thing I thought of at that time was
> the change in humidity in my darkroom due to the winter: from above 80 to below
> 50. Last week I started again with tests and tried to eliminate step by step
> the possible cause(s). By making new gum all problems were solved, but
> still...I checked the 'old' solution, no mould, nothing, looks quite normal.
Henk, my assumption would be that it was the gum, not the dichromate.
Because even tho dichromate solution may change with age, it gets weaker,
and the print still clears. (I found about 20% slowing in a year, but
since I print "by eye" most of the time anyway, doesn't matter much.)
Maybe the formaldehyde grew in the dark while you weren't looking. At
least, formaldehyde when it's too fresh, or too strong, interferes with
clearing in the manner you describe. I had similar bad results with an
aged gum mixed from scratch & preserved with formaldehyde. On the other
hand, there's also the possibility that your formaldehyde was too weak
and/or not enough & the gum went sour. How does it smell?
However, commercial lithographers' gum keeps indefinitely. I'm still using
the tail end of a gallon now nearly 20 years old and it's as good as ever
(also paler than the gum we get these days, BTW).
It hasn't been kept in a brown bottle, either, but in the now old musty &
crumbling frosted plastic container it came in. Are there any graphic
printers suppliers around town? Not that every single one of their 14
degree baume's is good, but I've only had one out of probably a dozen that
wasn't. And that one, come to think of it, was an etcher's gum, which
really is something else.
cheery Judy
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