Sil Horwitz (silh@iag.net)
Sat, 17 Apr 1999 12:56:08 -0400
At 99/04/17 07:50 AM -0700, you wrote:
>Their findings were for RC paper, the coating seemed to 'trap' the residue
>of cleared undeveloped silver halideds as in 'foxing' of poorly fixed,
>washed fiber based papers. The RC or resin coating on the paper acted as
>would a sealer to house the chemicls and allow the discoloration to become
>more and more vivid without possibility of cleaning as we can do with fiber
>paper.
The emulsion on RC papers is ON TOP of the plastic, not under it. In making RC
papers, high-grade paper is sandwiched between two layers of polyethylene,
polypropylene, or some other polymer that does not require a plasticizer. To
increase whiteness, the paper may be given a coating of stabilized titanium
dioxide (the pigment in weatherproof house paints) or baryta prior to making
the "sandwich." The emulsion, which is usually identical with that used on FB
papers, is then coated ON TOP of the plasticized paper, often requiring an
intermediate layer for adherence to the plastic coated paper.
In essence, as the paper is sealed by the plastic, RC paper requires less
fixing and washing time. In the initial enthusiasm, and the concern that
solutions could creep into the paper base in the middle of the "sandwich" and
could not be washed out, fixing and washing times were kept to the minimum
considered necessary. This has been changed somewhat, with only the commercial
snapshot processers (those that still wash at all, of course, as many are using
chemical stabilizers instead of washing, which requires a drain hookup) using
the fast fixing and wash times. Materials have improved since the first RC
papers were introduced, with the major problem of plastic degradation (not
emulsion problems) being solved to a large extent. Improvement are continuously
being made, but then that's technology today! Modern RC papers from major mfrs
can be considered to be as long-lived as FB, especially in harsh environments
which can affect paper.
Having said all that, I change from the technician to the artist, and say I
prefer papers which have some character, and, to me, RC papers have none!
Sil Horwitz, FPSA
Technical Editor, PSA Journal
silh@iag.net
Visit http://www.psa-photo.org/
Personal page: http://www.iag.net/~silh/
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