[pure-silver] Re: Emulsion hardening for reversal processing of 35mm B&W film

>
>
>    Formaldehyde is a VERY effective hardener. It is used in
>emulsion making and as a pre treatment for very alkaline
>processes that soften emulsions. An example of an auxillary
>hardener is:
>
>Kodak SH-1 Supplenentary Hardener
>Water                            500.0 ml
>Formalin*                         10.0 ml
>Sodium Carbonate, dessicated       5.0 grams
>Water to make                      1.0 liter
>
>*Formalin is a 40% Formaldehyde solution
>If monohydrated carbonate is used the amount is 5.9 grams.

<stuff clipped>

>
>    A more modern oganic hardener is Glutaraldehyde. This can
>be added directly to developers. It is added, for instance,
>to some of Grant Haist's monobath processes.
>

Note that Formaldehyde fumes are a powerful fogging agent, and 
Formalin shouldn't be stored or mixed anywhere near photosensitive 
materials. Apparently Glutaraldehyde is safer in this regard, though 
I don't have any first hand experience. Anchell and Troop give a 
formula for a Glutaraldehyde based hardener, as well as discussing 
adding it directly to developers.

The downside of Glutaraldehyde is that it is harder to come by than 
Formalin, especially since Eastman went out of the organic solvents 
business.
-- 

-tony

San Leandro, CA

http://www.shapesandshadows.com
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