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Re: platinum/palladium coating
----- Original Message -----
From: "Jeffrey D. Mathias" <jeffrey.d.mathias@worldnet.att.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Friday, April 06, 2001 8:58 AM
Subject: Re: platinum/palladium coating
> "Christina Z. Anderson" wrote:
> > What is the longest time anyone has gone successfully between
coating
> > the paper and exposing it?
> > Am I correct in assuming that the longer time will affect
contrast,
> > making it lower, and after a certain too long length of time, fog the
paper?
> > Should one use silica gel to keep the paper dry during storage?
>
> It is recommended that exposure commence immediately after finishing the
> coating (including drying). The coating can be dried to anywhere from
> 5% to 70% relative humidity and produce consistent excellent results
> (although different humidity can produce differences).
>
> A time of more than one hour between coating and exposing might cause
> some noticeable degradation. Four hours will definitely show
> degradation.
I would add that If you don't plan on exposing right away, keep the coated
paper as dry as possible. Humidity will hassen its deterioration ( fog ).
> Contrast may or may not be affected. Some observed degradation has been
> a loss of quality and substance, lessening of maximum blacks, a
> formation of graininess, fogging, and muddiness. Any combination of
> these may occur to varying amounts.
>
> I have tried hermetically sealing a coated paper and found it to still
> degrade the next day (even if kept in the freezer). Simply keeping the
> paper dry does not work as the coating seems to change over time alone.
>
> Also, I have had exposure times of between three to four hours which
> have worked OK, but I would not let the coating sit that long before
> starting the exposure (it will show degradation).
>
> Recommendation is to not store the coated paper. Plan on exposing
> immediately after coating is dried to desired level. Somtimes it can
> take 10 or even 15 minutes to dry the paper properly.
>
> Another important consideration is to apply the coating mixture
> immediatly after mixing. Do not mix a coating solution and let it sit
> around before coating as several things could go wrong.
>
I don't agree with this point. There are some mixtures that can sit for
several hours and produce better prints. You can certainly premix your
metal salts, but what ever you do, you will find that to get repeatable
results in speed, contrast, color, it is best to do it the same from coating
to coating. I have found that premixed sodium palladium and potassium
platinum will give warmer prints with lower contrast than freshly added
components to your ferric oxalate or ferric ammonium oxalate.
This gets into how you like to work and what you might find acceptable or
preferable. I have not tried it, but if you wanted to coat and dry and let
it sit, dry and in the dark for some time, perhaps a little extra oxalic
acid in the ferric might help slow down the fog.
Chris, Why do you want to let it sit? The overall effect of letting a
coating sit will depend on what was in the coating to begin with, type of
paper, how it was dried. You might find that with modification, a coated
and dried paper will work. What types of modifications? less soak in time,
higher drying temp without causing heat fog.....
EJ Neilsen