From: Jeff Buck (jeffbuck@swcp.com)
Date: 12/12/02-07:22:03 PM Z
I second all these responses from Sandy. I use the ammonium for film, but
sodium for alt where called for in the published procedures and such. For
film, you can't beat ammonium -- fixes much faster, washes much
faster. For the alt, I see little to gain by experimenting w/ ammonium. -jb
At 08:14 PM 12/12/2002 -0500, Sandy King wrote:
>Scot Wainer wrote:
>
>
>>Having been primarily a silver gelatin printer and concerned with
>>permenance, I began using Ammonium Thiosulfate based fixing baths for prints
>>after reading an article on the subject by Ilford. They recommended using a
>>film strength fixer for one minute to reduce the amount fixer absorbed by
>>fiber paper. Since I now work with a number of alt. processes requiring
>>fixing, recent readings have brought several questions to mind:
>>
>>1. What is the difference (strength wise) between Ammonium and Sodium
>>Thiosulfate? I remember reading somewhere (The Darkroom Cookbook?) that the
>>ammonium is about 40% stronger - is that about right?
>
>
>You may get more definitive answers on this but I will offer some
>observations based on my expereinces.
>
>
>Ammonium thiosulfate is widely available as a 40% solution. To make a
>fixer folks usually make a fairly concentrated stock and then dilute it
>for a working solution. For a liter of stock, for example, I mix 800ml of
>the 40% ammonium thisulfate with 5g of sodium metaborate and 20g of sodium
>sulfite, and top off to a liter. I dilute this 1:4 for a working solution.
>
>Sodium thiosulfate comes in the form of crystals that you mix with water
>to form whatever strength solution you need. For example, if you want a 5%
>solution, which is about what I have used for salted paper, VDB and
>kallitype, you simply mix 50g of sodium thiosfulate with a liter of water.
>A 10% solution would consist of 100g of sodium thiosulfate in a liter of water.
>
>>
>>2. Most reference materials list fixers based on Sodium Thiosulfate. Would
>>significant processing changes need to be made if I subsituted Ammonium
>>Thiosulfate?
>
>
>Faster fixing times.
>
>>
>>3. Would the use of Ammonium Thiosulfate cause prints bleach if the fixer
>>was made to the same strength as the one using Sodium Thiosulfate?
>
>
>Possibly. At the same strength the ammonium thiosulfate fixer works much
>more rapidly.
>
>Frankly, I avoid the issue by using both types, an ammonium thiosulfate
>fixer for films and modern silver papers, and a sodium thiosulfate fixer
>for alternative work.
>
>Sandy King
>
>
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