[pure-silver] Re: Purple-Tinted Negs
- From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 1 Jun 2006 12:05:33 -0400
Does this warning extend to other uses of thiourea since it is used in
several toning formulas?
-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Ryuji Suzuki
Sent: Thursday, June 01, 2006 11:48 AM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: Purple-Tinted Negs
From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
Subject: [pure-silver] Re: Purple-Tinted Negs
Date: Thu, 1 Jun 2006 09:48:56 -0400
> A simple reducer for dichroic fog can be made from 12 g of thiourea
> and 12 g of citric acid per liter. From Glafkides, Vol I. It also
> mentions using formalin to harden the emulsion before using any
> solution containing thiourea. This is probably more active than the
> acidified fixer.
This is not recommended. Thiourea slowly decomposes on silver surface
with light and this makes acid that is corrosive to silver image.
Thiourea can't be washed from silver surface by water wash and it will
stay once it is applied. Many daguerreotypes were killed by this kind of
treatment.
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