From: Jeffrey D. Mathias (jeffrey.d.mathias@worldnet.att.net)
Date: 04/15/00-04:28:38 PM Z
"Robert W. Schramm" wrote:
> ...
> I have also noticed that platinum is very sensitive to humidity. I
> have found that problems seem to emerge when the humidity is very
> low. ...
Pt/Pd is sensitive to humidity, but not so as to cause problems unless
the relative humidity becomes greater than 80% (or greater than 70% when
the temperature is above 70F). Low humidity works fine, and I have
never had a problem because of low humidity. However, one must adjust
their procedures when working at various humidities. Also various
desirable effects in the print may only be produced by certain humidity
conditions.
I have found Pt/Pd to be critically sensitive to higher temperatures
during coating. I have worked at ambient temperatures as low as 50F (a
bit uncomfortable) with excellent results. The same results can be had
up to a temperature of about 70F. At temperatures above 70F
deteriorating results are observed (and worse for higher relative
humidity). Above 75F and definitely above 80F most thicker papers and
papers with greater surface texture are not worth coating. The coating
is superior, smother, and easier when done at an ambient temperature
below 70F. Note though that some solutions of the metal salts may
require a warm water bath to keep them in solution. The temperature of
the chemicals is a different mater from the ambient temperature during
coating.
I have found that a temperature above 140F during exposure can cause
problems when platinum and sodium are in the coating. Potassium (or
lithium or ammonia) can be sustituted for any sodium but will provide
differing results.
Also a hot contact printer can play havoc with high RH coatings.
My suggestions are:
a) find the adjustments to procedures or materials to work at various
relative humidity (less than 70%) and take advantage of the variety of
results possible.
b) coat at a comfortable temperature below 70F.
c) Keep the contact printer cool and exposures less than 140F (or less
for high RH coatings).
-- Jeffrey D. Mathias http://home.att.net/~jeffrey.d.mathias/
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