[pure-silver] Re: Adding Sodium Sulfite to Sodium Thiosufale.
- From: Gerald Koch <gerald.koch@xxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sat, 2 Apr 2011 15:29:53 -0700 (PDT)
Sodium sulfite is not needed unless that hypo solution is acidified in some
manner. If you don't use an acid stop bath you won't need it. When acid is
added to a sodium thiosulfite solution colloidal sufur is produced. The
sulfite
ions combine with the sulfur to regenerate thiosulfate ions.
There is a classic chemistry demonstration called "the setting sun." A beam of
light from a slide projector is passed through a thiosulfite solution onto a
screen. It looks like the sun. Then, with stirring, a small amount of acid is
added. The "sun" becomes more and more reddish in appearence as colloidal
sulfur scatters the light. It looks like the sun is setting. This scattering
is of course exactly what happens to the real sun as it reaches the horizon.
The light must pass through more of the atmosphere with greater scattering of
the shorter wavelengths.
Jerry
________________________________
From: Bogdan <bkarasek@xxxxxxxxxxxx>
To: pure-silver@xxxxxxxxxxxxx
Sent: Sat, April 2, 2011 5:48:17 PM
Subject: [pure-silver] Adding Sodium Sulfite to Sodium Thiosufale.
hi all,
In the discussion on using 2 bath Sodium thiosulfate, someone mentioned adding
Sodium sulfite to prolong the keeping properties of simple hypo.
I'm using Anchell's "Darkroom Cookbook" as my reference for my chemistry.
For plain hypo, He recommends 480.0 grams of Sodium Thiosulfate per 2 L of
water; how much Sodium sulphite should I add to assure longevity.
Till now, I have never added Sodium Sulfite to the hypo and would tone the
prints in 1:9 KRST (no additives) and then wash.
Any suggestions of the amount I should add to the hypo?
Cheers,
bogdan
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