----- Original Message ----- From: "Mike Kirwan" <mkirwan@xxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, January 27, 2011 6:50 PM
Subject: [pure-silver] Re: Oh How I Miss This Paper
Portiga was a different paper, nice, but not the same as Record Rapid.
I still have some Portiga in my collection, has a different surface
than RR.
If my memory serves me correctly, one of the reasons for the demise
of these
papers was some of the chemicals in the emulsion, I believe that both
RR and
Portriga had a Cadmium component; which was also in some of the
famous and
long lamented Kodak papers :(
Mike
I will have to look at the old ads. RR was advertised in the
British Journal Almanac, I think and it seems to me it was identical
to something sold by Agfa under a different name here.
I think the chemical was a cadmium compound. I one of the members
of this list is Dave Valvo who designed papers for Kodak. I am not
sure he still follows it. He would know definitely what had to be
changed because of environmental regulations. Whatever was done it
seems to affected the shelf life of raw stock and also seems to have
affected warm tone emulsions more than neutral or cold tone ones.
Emulsion making as described in some of the older books is highly
simplified. Its a very complex process with many additives. The
chemistry is way beyond me. A lot of the popular wisdom about it is
either out of date or was never correct. For instance, the amount of
silver in the emulsion has little or nothing to do with the way the
final image looks. I think Kodak had the most advanced emulsion making
technology in the world but not always the best looking papers
although they had the most consistent emulsions and most uniform
surfaces. Anyone who has had to deal with the frilling and cockeling
of Agfa papers knows what I mean.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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