----- Original Message ----- From: "Claudio Bonavolta" <claudio@xxxxxxxxxxxx>
To: "Pure-Silver" <pure-silver@xxxxxxxxxxxxx> Sent: Thursday, February 18, 2010 4:15 AM Subject: [pure-silver] Non-acid rapid fixer - continued
Following my quest for a non-acid rapid fixer due to my sensitivity to sulphur dioxyde, I would like to thank all of you who replied either through the list or directly.A simple formula for a sodium thiosulfate fixer is as follows. For rapid fixer ammonium thiosulfate is substituted for the sodium thiosulfate in appropriate amount. Ammonium thiosulfate is usually sold as a liquid concentrate because the powdered version has a short shelf life.I finally got the raw chemicals and modified my process to:- developer - citric (15gr/l) acid stop bath - rinse - Kodak F-9 modified (see below) fixer in 2 baths - rest of the process The original F-9 formula is the following: Water 600ml Hot waterSodium Thiosulfate 360gr crystalline or 230gr anhydrousAmmonium sulfate 60gr Sodium Sulfite (anhydrous) 15gr Acetic Acid glacial 13.5ml Boric Acid 7.5grPotassium Alum (fine dodecahydrated) 15gr Do not use anhydrousCold water to make 1000mlAs you can see, it's a hardening formula which I don't need.The simplified formula I use is the following: Water 600ml Hot waterSodium Thiosulfate 360gr crystalline or 230gr anhydrousAmmonium sulfate 60gr Sodium Sulfite (anhydrous) 15gr Cold water to make 1000mlBob Kiss suggested to add 5gr/l of sodium metaborate as to keep the solution on the alkaline side. As I wasn't able to find the metaborate (tried two chemical distributors, both were out of stock ...), I started without it, will add it later. The good thing is that, as the dilution of the sodium thiosulfate looks endothermic (absorbs heat), the temperature cools down and you can use it quickly after. So, no need to prepare it long in advance.I was also looking for a fast fixer. Fast fixers are normally based on ammonium thiosulfate but F-9 is described as being fast *and* based on the more readily available sodium thiosulfate. So I compared the F-9 modified formula to Ilford Rapid Fixer at 1+4 (typical film strength) by putting a film leader in each and measuring the time it took to clear. I used of course the same film type from the same lot (from a bulk roll) and the temperature of both fixers was identical. The clearing was just slightly slower, a few seconds, in the F-9, so, from a practical point of view, I just keep the same fixing times. Looks like the ammonium ions coming from the sulfate are making the difference but my limited chemical skills do not allow me to be affirmative on this.For those who tone the prints in selenium, because the fixer is no more acid, the risk of stains has gone and there is no need to wash the prints between the fixer and toner, I just put a rinse between them.I continue to use a washaid (sodium sulfite @ 20gr/l discarded at the end of the session) before the final wash as to keep the wash times and water consumption at the minimum.On the smell and sulphur dioxyde side, I'm really happy, my lungs confirmed this is the way to go ... Note that before the non-acid fixer, I tried also to put a rinse between the stop bath and an acid fixer and it already diminished the quantity of sulphur dioxyde that was released but there was still some coming from the fixer alone.The next steps on the fixer side are to put in place an efficient and practical way of measuring the exhaustion of the fixer and quality of the fixing. I was used to use the potassium iodide test (very easy to do) but seen the recent "Fixer test vs fixer test" discussion, I'll have to re-think it and try to see if I can relate in some ways a more accurate test but more cumbersome (selenium test) and the easy potassium iodide test.Claudio Bonavolta http://www.bonavolta.ch
Simple non-acid, non-hardening fixing bath. Water 500.0 ml Sodium thiosulfate, crystalline 240.0 grams Sodium sulfite, desiccated 5.0 grams Water to make 1.0 literThe sulfite can be increased up to about 15 grams/liter to permit the use of an acid stop bath. The additional sulfite will prevent decomposition of the thiosulfate by the acid. A citric acid stop bath can be used with this fixer. However, any acid carried over into the fixer may result in some sulfur dioxide being emitted.
-- Richard Knoppow Los Angeles, CA, USAdickburk@xxxxxxxxxxxxx
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