[pure-silver] Re: Selenium toning + Agfa Sistan

From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
Subject: [pure-silver] Re: Selenium toning + Agfa Sistan
Date: Tue, 30 Nov 2004 14:56:44 -0800

>    I will also add that complete conversion may not be 
> necessary for maximum image protection by the toner. IPI 
> recommends a 60% conversion for its polysulfide toner as 
> determined by densitometric testing. This is not to say that 
> this is better than complete conversion, only that the 
> criterial of complete conversion may be someone's guess not 
> based on testing.

Degree of toning necessary for certain stability criterion depends on
the emulsion and possibly on the developer. See the Johnsen and
Pedersen's paper.

That 60% conversion criterion was set because highly acceptable
duplicate of microfilm could be made from microfilms with 60% of the
original density remaining after degradation. It was not chosen
because this magic number somehow maximizes the degree of protection.

>    Also, microfilm is not the same as pictorial film or 
> printing paper. The requirements for toning it are that the 
> crystal structure not be changed enough to destroy any data. 
> This is not a criteria for pictorial photography where 
> different toners and amounts of toning are acceptable.

Photographic prints could be toned more deeply than microfilm if
desired. The emulsions used for microfilms and enlarging papers are
not that dissimilar. I would take warnings from microfilm conservation
scientists to apply to photographic prints unless otherwise proven.

In conclusion, I would not trust anything but polysulfide (with or
without selenium) toner for my final prints. It's easiest and most
effective.
--
Ryuji Suzuki
"Keep a good head and always carry a light camera."
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