From: Ryuji Suzuki (rs@silvergrain.org)
Date: 09/23/03-05:33:36 PM Z
From: Jean-Paul Gandolfo <jpgalt@infonie.fr>
Subject: Autochrome centenary
Date: Wed, 24 Sep 2003 00:41:34 +0200
> We have made some modern (and alternative) tricolor screens used to
> produce color plates with an assembly method (black & white ilford
> FP4 + reversal developed, exposed behind the screen, removed,
> developed and registered again with our screen). The result was't
> as good compared with the original plate.
I suspect there are a few possible problem areas here. It's not meant
to be a criticism or anything, but just what I can offer for
experimentalists based on what I got from your message combined with
reading on emulsion literature and my limited emulsion making
experience.
Autochrome emulsion shoud be somewhat high silver content (in terms of
g AgNO3 per liter of emulsion) and coated very thin (the overall
coating weight is about same as regular plates) right next to the
color matrix. In the emulsion literature, scatter effects and parallax
are said to be problematic if this requirement is not satisfied.
Also, FP4+ film has layers of coating including overcoat, making it
difficult to ensure tightest contact between photosensitive layer and
color matrix layer.
Dimensional stability and freedom from curling are also very critical
requirements with Autochrome matrix since we are talking about
registration tolerance on the order of 10 microns from end to
end. Based on typical specs in the literature, I think only glass
would be satisfactory for the supporting material for this
process. Also, I don't think removing the film for processing and
registering again is a viable option.
In addition to that, in order to get good color rendition, shadow
areas of the emulsion must be packed with very fine grains, which is
best realized by custom making the emulsion.
So, I think your prototyping from factory made material was valuable
experience, but I also think you might have got much better result if
you could seek a help from a local emulsion maker.
-- Ryuji Suzuki "Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)
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