[alt-photo] Re: HYDROSCOPIC!

[Richard Knoppow]

----- Original Message ----- 
From: "Marek Matusz" <marekmatusz at hotmail.com>
To: "alt photo" 
<alt-photo-process-list at lists.altphotolist.org>
Sent: Monday, May 10, 2010 6:19 PM
Subject: [alt-photo] Re: HYDROSCOPIC!


>
> Bob,
>
> My two cents from the chemistry perspective are similar to 
> Ryuji's. Ammonium thiocyanate is a complexing agent for 
> gold. It is a common problem for gold toners to keep gold 
> in solution for prolonged periods of time. ANd while the 
> thiocyanate bases toners are faily stable, they will 
> eventually plate the gold in the bottle loosing their 
> potency. They are best used just after the addition of 
> gold. Get a batch of prints and tone them all at one 
> session. I kept a bottle of a thiocyanate toner for yers 
> and it had a lot of gold sediment in it.
>
> You can just add more gold to replenish the toner, as all 
> other reagents are in large acess.
>
> It really matters little if you add 25 or 50 grams of 
> solid ammonium thiocyanate(I actually have not tried that, 
> so final judgement is in the experiment), but have used 
> thicyanate gold toners exstensively in my silver B&W past. 
> Interestingly enough just before final collapse of B&W 
> chemistry Agfa introduced a silver image stabilizer that 
> was thiocyanate based, but I did not really follow that 
> and I think Agfa dropped their silver B&W chemistry. So 
> perhaps both components can act to stabilize silver image, 
> but gold will also change the colour
>
> The toner might be sensitive to the presence of fixers, so 
> an extensive wash might be necessary to prolong its life, 
> maybe somebody else might comment. But if you are using it 
> in a batch mode, that is add gold and tone a bunch of 
> prints at one time it might not matter a lot. Let us know 
> in any event.
>
> Marek
     I believe you are thinking of AGFA Sistan, it was 
actually on the market for a number of years. I don't have a 
bottle handy but I think it contained Potassium thiocyanate 
and a wetting agent. AGFA changed their recommendations for 
its use a couple of time. Too much could result in staining. 
I was never able to find anything in the scienfific 
literature proving its effectiveness. Fuji also sold a 
non-toning stabilizer but I don't know what was in it and it 
was, AFAIK, sold only in Japan. Ryuji may know more about 
both of these.

--
Richard Knoppow
Los Angeles, CA, USA
dickburk at ix.netcom.com