[alt-photo] Re: HYDROSCOPIC!

[Marek Matusz]

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
 
> Date: Mon, 10 May 2010 18:02:24 -0400
> To: alt-photo-process-list at lists.altphotolist.org
> From: rs at silvergrain.org
> Subject: [alt-photo] Re: HYDROSCOPIC!
> 
> Dear Bob,
> 
> I bet ammonium thiocyanate is there as a ligand for gold, and
> for this purpose, thiocyanate in this formula is in excess. If
> I were to make a small bet (well, that's less than $10 worth
> of gold, I guess :-), the amount of ammonium thiocyanate is
> not critical.
> 
> Also, ammonium thiocyanate is not used as an alkaline agent in
> this formula. I don't think pH would be a good assay for
> it. If anything, I think specific gravity would be more
> useful. If you can measure specific gravity of, say, 25%
> solution, and adjust your stock to match that value, I think
> it'd be close enough for your purpose.
> 
> Ryuji
> 
> --
> Ryuji Suzuki
> "The essence of the beautiful is unity in variety." (Felix Mendelssohn)
> 
> From: "BOB KISS" <bobkiss at caribsurf.com>
> Subject: [alt-photo] HYDROSCOPIC!
> Date: Mon, 10 May 2010 11:50:18 -0400
> 
> > DEAR LIST,
> > 
> > Can anyone help me with the following?
> > 
> > I want to mix some Ammonium Thiocyanate gold toner. Bloody Ammonium
> > Thiocyanate is seriously hydroscopic. The sealed plastic env in the B&S
> > toner kit is liquid! No problem here because it is premeasured to make a
> > small amount of toner. However, the local university which is happy to get
> > rid of their supply has two 500g bottles of Ammonium Thiocyanate that are
> > both liquid!!! No one can say for sure if any has been taken from the jars
> > so no way to be certain of the concentration. 
> > 
> > I see no reason I can't use these liquid Am Thio solns from the
> > bottles but I need to know when I have added enough per liter for the toner.
> > I am betting that all these alkaline salts (Borax, Amm Thio, etc.) are
> > mainly to set the pH for the gold toner which determines the resulting
> > particle size and hence color. Might it be possible to determine the
> > correct pH in the liter of the alkaline soln and simply add the soln from
> > the bottle to, let's say, 800 ml of distilled water until it reaches that
> > pH? Adjust vol & more Amm Thio to 1 liter at the correct pH? 
> > 
> > Of course, the trick question is, what IS the correct pH?
> > 
> > 
> > 
> > The formula from Chris James' book is:
> > 
> > 
> > 
> > 800 ml dist water
> > 
> > 25g Ammonium Thiocyanate
> > 
> > 2g Tartaric Acid
> > 
> > 5g Sodium Chloride
> > 
> > 20ml 1% gold chloride soln
> > 
> > 
> > 
> > Any ideas?
> > 
> > CHEERS!
> > 
> > BOB
> > 
> > 
> > 
> > _______________________________________________
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