Re: Bromo-iodide Silver Gelatin Emulsion as an Alternative process

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From: Ryuji Suzuki (rs@silvergrain.org)
Date: 07/24/03-03:28:47 PM Z


From: Scott Walker <walker@sympatico.ca>
Subject: RE: Bromo-iodide Silver Gelatin Emulsion as an Alternative process
Date: Thu, 24 Jul 2003 14:37:41 -0400

> I was going to say that the dyes themselves are not mysterious, but
> the way there used and the recipes and concentrations are.

That's what I said. But we can't complain for the lack of published
recipe for full spec modern emulsions as it would be a silly idea to
think about making one in your basement two decades ago. To me, only
now the idea of making silver gelatin material sounds very appealing.
All but a few favorite enlarging papers and films disappeared from the
market. Now we are betting on which is the next one to be gone. Plus
we want to be creative about the material.

The use and effect of dyes are affected by the other specs of the
emulsion like the crystal shape, the method of chemical sensitization,
etc. and because there is a great degree of variability in everything,
I wouldn't be surprised by the lack of specifics in publications. Like
anything else, you gotta try! Think about the range of pAg and pBr in
your kettle while precipitating and ripening, and the range of mixture
of crystal sizes and shapes. I think it would be unreasonable to
expect an one-fits-all dosage recommendation.

> In fact most of the sensitizer dyes can be de-sensitizers used at
> the wrong time or in the wrong quantity.

I think fogging problems are more likely.

> But I take that back, the dyes are mysterious! I have spent about 6
> months on a Dye called Orthochrome T mentioned in Wall's book. So if
> you want a challenge we can compare notes...

I don't know Orthochrome T is still in use or available, or
corresponds to what name in modern nomenclature. It is a primarily
green sensitizer but posses high orange and red sensitivity, so it is
considered a panchromatic dye in old literature.

Modern literature goes with more systematic names. I recommend the
article written by David Sturmer of Eastman Kodak, and Roderich Raue
of Bayer AG. Raue's article covers methine dyes among others.

Other starting points are articles by people like Gilman or Tani in
Photographic Science and Engineering, Journal of Imaging Science, etc.
A big leap in dye sensitization was in mid 60's, so I'd consider
literature newer than that date.

I still think the biggest challange is to work under total darkness
with no automation. I would appreciate anyone's insight about this
issue.

--
Ryuji Suzuki
"Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)

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