[pure-silver] Re: Sodium Bisulfite
----- Original Message ----- From: "Justin F. Knotzke" <jknotzke@xxxxxxxxxx> 
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, October 25, 2007 3:29 AM
Subject: [pure-silver] Re: Sodium Bisulfite
On 24/10/2007, Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote: 

    Bisul _fate_ and bisul_fite_ are not the same thing.
Bisulfate is strongly acid and is often found in drain
cleaners.
Sorry Richard, I do in fact have Sodium Bisulfite.. My apologies.. 


   I suspect Lootens copies Kodak F-24 an acid

non-hardening fixing bath.

Kodak F-24
Water (at 125F or 52C)                        500.0 ml
Sodium Thiosulfate, crystalline 240.0 grams 
Sodium sulfite, desiccated                     10.0 grams
Sodium bisulfite                               25.0 grams



Water to make                                   1.0 liter
I'm a bit confused with the amounts of water.. Are we trying to make 
1.5L of actual workable solution ?
I'm trying to make a concentrate for a 3L bottle. I don't want to have to mix from scratch each time but to just add water and go.. 

   Thanks again,

   J
This is to make 1 liter of working solution. I don't know how concentrated it can be made, the limit would be the saturation point of the thiosulfate. Where it says "water to make" in a formula it means to add water to the mixed solution to bring the total up to whatever the amount is. I usually quote formulae standardized to make 1 liter so that any amount can be made up by simply multiplying or dividing the various amounts. Nearly all published fixer formulas call for crystalline thiosulfate but if you can obtain the anhydrous variety mixing is easier because it does not cool the water as it goes into solution. Using freshly made up fixer each time sounds like a good practice but it may actually be better to use a two bath system and re-use the fixer. Especially for prints the capacity of a single bath to achieve archival fixing is very limited. Ilford figures are only 10 8x10 sheets per _gallon_. By using two successive fixing baths the capacity is multiplied by four to ten times. The use of a sulfite wash aid will further extend the capacity since it will release some adsorbed silver-thiosulfate complexes from the emulsion. The ability of a fixing bath to completely convert the undeveloped halide to a completely soluble form depends on how many free thiosulfate ions are available. It takes three thiosulfate ion to convert one halide molecule. The ability of the fixer to fix depends on how much silver it has absorbed. In a two bath system the second bath remains relatively fresh so it can complete the conversion of any halide left from the first bath to a soluble form. There are three methods of testing fixing baths for condition: The first is the well known potassium iodide test. The iodide converts some of the complexed silver to silver iodide which appears as a cream colored precipitate. This test works but is difficult to calibrate to a definite rejection point. The second test is to measure the clearing time for film. A standard film is used and the clearing time measured with a fresh bath. Subsequent tests are made the fixer being rejected when clearing time doubles. I think this probably results in an optimistic measurement and is difficult to do with paper. The third way is to test a fixed out sample for residual silver. The test solution is an about 2% solution of sodium sulfide. The sulfide will "tone" any silver halide remaining in the film or paper resulting in a yellow or brown stain. Under certain circumstances a 1:9 dilution of Kodak Rapid Selenium Toner will also work, however, the film or paper must be washed essentially free of hypo or the test fails. The sulfide test is not affected by the presence of hypo. The KRST test has the advantages of long solution life and lack of odor. 

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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