Date: 27 Feb 96 17:20:57 EST
From: Pollmeier Klaus <100561.2417@compuserve.com>
To: Multiple recipients of <alt-photo-process@vast.unsw.edu.au>
Subject: Re:PVA
Thanks to Paul Simon for his information. I just found an old book on
Polyvinylalcohol here which I should have read before I sent the mail. So if
somebody run into problems with a certain PVA: There are probably even more
types of PVA than types of gelatin, with even stranger physical/chemical
properties:
The water solubility of Polyvinylalcohol depends on its degree of
polymerisation. The higher the degree, the lower the solubility. The content of
polyvinylacetate also has a certain influence on the solubility: With more than
5% it becomes insoluble in cold water, but soluble at 65-70 deg. C. With 20% it
is soluble only at 35-40 deg. C. and it will stay liquid even while cooling
down. With 40% it is soluble at room temperature, but falls out at 30-35 deg. C.
With more than 50% polyvinylacetate content PVA is insoluble in water.
S. th. more interesting for practical work: Developing dichromated PVA coatings
will be easier, if 0.5% ammoniumthiocyanate is added to the PVA. Even
overexposure or tanning caused by too long waiting before development can be
compensated by a little thiocyanate in the dev. water.
Klaus Pollmeier
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