[pure-silver] Re: Thiourea and Thiourea dioxide
- From: Ray Rogers <earthsoda@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Thu, 24 Feb 2011 07:41:10 -0800 (PST)
It was indeed!
I remember the material from way back when... but only after reading your post!
Memory is strange in that it frequently exists once we are reminded of it...
I wish money was like that!
Ray
--- On Thu, 2/24/11, C.Breukel@xxxxxxx <C.Breukel@xxxxxxx> wrote:
From: C.Breukel@xxxxxxx <C.Breukel@xxxxxxx>
Subject: [pure-silver] Re: Thiourea and Thiourea dioxide
To: pure-silver@xxxxxxxxxxxxx
Date: Thursday, February 24, 2011, 3:25 PM
..ah I see now, sorry..but I hope my post was interesting nevertheless..:-)..
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Ray Rogers
Sent: donderdag 24 februari 2011 16:17
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: Thiourea and Thiourea dioxide
Cor,
(Hi!)
I think Jerry is addressing a different issue here....
(OTOH, I might be dreaming... I am so sleepy.)
--- On Thu, 2/24/11, C.Breukel@xxxxxxx <C.Breukel@xxxxxxx> wrote:
From: C.Breukel@xxxxxxx <C.Breukel@xxxxxxx>
Subject: [pure-silver] Re: Thiourea and Thiourea dioxide
To: pure-silver@xxxxxxxxxxxxx
Date: Thursday, February 24, 2011, 2:58 PM
I do not believe that is true in this case, Jerry, its not about pH but about
development:
I quote Tony again:
Thiourea dioxide, also known as formamidine sulphinic acid (FSA for
short) is a common chemical used in the textile industry as a bleach in the
dyeing process. It has replaced the more toxic hypochlorites, as it is
safer and does less damage to the environment.
The process is simple and the chemistry relatively safe. In fact
thiourea dioxide is much safer than its chemical cousin, thiourea (as used
in odourless sepia toning kits), which is a suspected carcinogen. The
technique is applicable to both resin coated and fibre based prints and,
because the result is a print which is composed of just colloidal silver,
the image can be subsequently toned or returned to its original state. One
major advantage of FSA over the usual bleach and tone formulae is that
there is no loss of image density, if used with the correct beach. In fact,
there is an intensification of the shadow tones with no loss of highlight
density.
FSA is a powerful reducing agent whose application to monochrome
printing was discovered by George Wakefield a couple of decades ago. When
mixed in solution with an alkali, it will reduce the rehalogenized image
back to metallic silver with variable particle size, and therefore colour.
Best,
Cor
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Gerald Koch
Sent: donderdag 24 februari 2011 15:37
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: Thiourea and Thiourea dioxide
Sodium bisulfate (sodium hydrogen sulfate) can be substitued for sulfuric acid
in many photo formulas. It has the afvantage of being a solid and hence safer
to use than the acid. It can be obtained from many sources. It ir sold as
pH-Minus for adjusting the pH of swimming pools.
Jerry
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