From: Judy Seigel (jseigel@panix.com)
Date: 08/03/03-10:23:58 PM Z
On Sat, 2 Aug 2003, Richard Sullivan wrote:
> .... It is my understanding that all
> of this staining mumbo jumbo is simply related to paper sizing. At APIS
> Stuart said that you could make anything >>not<< work and went on to say
> that he and Kerik had made every pigment they had tried work, and by
> working he was referring to not having any stain. Stuart came by the lab
> numerous times and discussed his progress and I recall that he eventually
> found out that staining was all due to poor sizing.
Most human events are multiply determined, and so, in my experience, is
pigment stain. Although it's rare (I find) with *properly* sized paper and
a compatible gum, I've found that changing ONLY ONE FACTOR, that is, the
GUM, can cause the stain from hell. Ie, one set of ingredients didn't
stain with gum A and did stain with gum B, yet gum B was fine with a
different paper and/or pigment and/or size.
I haven't seen mention of which gum Stuart Melvin used. If he did all his
tests with the same gum, he may have over-generalized. Another gum might
perform differently in some, or many, respects.
> I too have my treasured copy of Kosar and have noted the section that talks
> about incompatible pigments with chromium. The main one was is ultramarine.
> Despite Kosars references I did not see any degradation of ultramarine with
> chromium in carbon printing. It is quite transparent compared to thalo and
> uses up a ton of pigment, an issue when you are coating 75 sq feet at a time.
>
> Many of the references in Kosar are a bit suspect in my mind. Not unusual
> for a compendium work of this nature. Kosar is regurgitating tons of info
> and obviously has not tested everything himself. All in all it is an
> excellent source book even if the colloid chromium chapters is a bit thin.
Odds are that any ultramarine in Kosar's tests was a very different
chemical from the "ultramarine" in our paints today. Does Melvyn say which
"ultramarine" he tested?
And, as I've said before, most of the tests Kosar cites were done for
carbon or related processes. The assumption that effects would be the same
with gum is wrong (for example the claim that gum would print "straight
line" because carbon does). Second, Kosar's pages are studded with terms
like "presumably," "probably," and "apparently." These are probably
worthwhile observations, but counterproductive when taken as settled
broadband fact.
Judy
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