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alternatives for ammonium thiosulfate?
On Monday, July 9, 2001 5:45:19 AM UTC-4, Klaus Schmaranz wrote:
Hi, Ammonium thiosulfate is quite difficult to get (and expensive!) because it's quite unstable... sofar, so good... Is there any alternative to be used for a fixer that will be capable of fully fixing modern emulsions (such as rapid fixer)? Sodium thiosulfate doesn't do a perfect job on them, at least not if they contain silver-iodide. BTW - is there any source where I can find out which films and papers need ammonium thiosulfate because of the iodide, and which don't? Thanks, Klaus. There is a tiny but growing sub-culture alternative to ammonium thiosulfate as a fixer, not spoken of in polite erudite professional spaces. Everybody knows this elephant in the room is as brown as Cafenol-C. Pardon my vulgarity, but iodized Sea Salt or Portuguese Kitchen Salt (NOT TABLE and NOT REFINED) plus distilled water supersaturated and filtered at 1.2 kg/litre density at 25-40 degrees C for 4 to 18 hours has been used with some degree of success. An odd thing is that a particular seaweed called "Dulse", rich in potassium iodide, may be added to the soup for an extra special secret "kick". Of course that's off the main highway off some back road of electronic information, face down in a ditch with a tinfoil hat kind of stuff. Not exactly something you would use for a Presidential inauguration or anything other than art. You didn't here it from me! Keep it on the D-L! |
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alternatives for ammonium thiosulfate?
"Jean-David Beyer" wrote in message ... On 11/21/2013 01:47 AM, wrote: On Monday, July 9, 2001 5:45:19 AM UTC-4, Klaus Schmaranz wrote: Hi, Ammonium thiosulfate is quite difficult to get (and expensive!) because it's quite unstable... sofar, so good... Is there any alternative to be used for a fixer that will be capable of fully fixing modern emulsions (such as rapid fixer)? Sodium thiosulfate doesn't do a perfect job on them, at least not if they contain silver-iodide. BTW - is there any source where I can find out which films and papers need ammonium thiosulfate because of the iodide, and which don't? Thanks, Klaus. There is a tiny but growing sub-culture alternative to ammonium thiosulfate as a fixer, not spoken of in polite erudite professional spaces. Everybody knows this elephant in the room is as brown as Cafenol-C. Pardon my vulgarity, but iodized Sea Salt or Portuguese Kitchen Salt (NOT TABLE and NOT REFINED) plus distilled water supersaturated and filtered at 1.2 kg/litre density at 25-40 degrees C for 4 to 18 hours has been used with some degree of success. An odd thing is that a particular seaweed called "Dulse", rich in potassium iodide, may be added to the soup for an extra special secret "kick". Of course that's off the main highway off some back road of electronic information, face down in a ditch with a tinfoil hat kind of stuff. Not exactly something you would use for a Presidential inauguration or anything other than art. You didn't here it from me! Keep it on the D-L! I used to use F-9 fixer. It is not as fast as Kodak Rapid Fixer, but it is faster than F-5. Water 600ml Hot water Sodium Thiosulfate 360gr crystalline or 230gr anhydrous Ammonium sulfate 60gr Sodium Sulfite (anhydrous) 15gr Acetic Acid 28% 48ml Boric Acid 7.5gr Potassium Alum (fine dodecahydrated) 15gr Do not use anhydrous Cold water to make 1000ml It is a hardening fixer. If you do not want hardening, you could reduce or omit the Potassium Alum. I prefer F-6 fixer for most things. Water, about 50 Celsius (125° F.) 600 ml Sodium Thiosulfate (Hypo) 240 g Sodium Sulfite, desiccated 15 g Acetic Acid, 28%; 48 ml Kodalk 15 g Potassium Alum 15 g Cold water to make 1 liter Here, too, you can omit the potassium alum if you do not need hardening. You left out Kodak F-7 Rapid Fixer Water, about 125F (50C)......................600.0 ml Sodium Thiosulfate, crystalline..............360.0 grams Ammonium Chloride.............................50.0 grams Sodium sulfite, desiccated....................15.0 grams Acetic acid, 28%..............................48.0 grams Boric Acid, crystalline....................... 7.5 grams Potassium alum................................15.0 grams Water to make..................................1.0 liter As with the other formulas the alum can be left out and probably the acid too if you don't want a hardening fixing bath. Sodium thiosulfate, desiccated, can also be used with an adjustment in the amount. A couple of general notes on fixing baths: Sodium thiosulfate will do fine for iodide-containing emulsions but the fixing time should be extended somewhat. Nearly all film emulsions contain some silver iodide and many modern paper emulsions do also. Iodide is both more difficult to fix and iodide accumulated in the fixing bath tends to retard fixing. The usual rule is to fix for twice the time it takes the emulsion to visually clear. This rule works for reasonably fresh fixing baths. However, an exhausted bath will not completely convert silver halide to soluble silver no matter how long fixing is extended. At one time Kodak recommended extending fixing time to three times clearing time for tabular grain films, which have a lot of iodide and are difficult to fix. The solution is to use a two-bath fixer. Ammonium fixing baths have greater capacity before they stop fixing effectively and some experts state that a two-bath fixer is not necessary if a "rapid" fixer is used, but I think its wisdom as well as an economy to use a two bath system. In addition, the use of a sulfite wash aid (I think Ilford still sells this but you can make your own) will cause some otherwise insoluble silver complexes to wash out. It effectively extends the capacity of the fixing bath. Wash aid will also remove residual sensitizing dye from films where it is persistent such as T-Max. Kodak used to state that the stain was the result of the dye binding to the silver due to insufficient fixing but I've encountered this staining even with very extended fixing in fresh fixer. The wash aid removes it in a few seconds. Non-acid fixing. Unlike developers, which must operate at a certain pH to work, fixing baths are pretty much independent of pH. What the acid in a fixing bath is for is two-fold; first, it stops the developer, and secondly it is necessary for the non-organic hardeners usually used in fixing baths. If the hardener is not necessary it can be left out and the acid can be left out also. While I think it is probably a good idea to have a certain amount of buffered acid in the fixing bath to eliminate development while fixing it is not necessary. However, a thorough rinse in place of the usually acid stop bath is a good idea. Most of the sodium sulfite in fixing baths is there to prevent the acid from decomposing the thiosulfate. If the bath is made neutral most of the sulfite can be left out, but not all. For one thing it prevents staining from carried over developer which may remain active in the fixing bath, and also it prevents decomposition of the thiosulfate from other sources such as exposure to the air. Typical fixing baths have about 15 grams per liter of sodium sulfite, if made neutral about 5 grams will do although there is no harm in using more and it might result in cleaner negatives by preventing any staining. I can see no advantage whatever to making a fixing bath alkaline. The advantages of a non-acid bath are obtained if its neutral and it will have less tendency to re-activate carried over developer. If a buffered sulfite wash aid is used following fixing there are really no advantages to a non-acid or non-hardening fixing bath other than the lack of odor. Also, Ilford makes rapid fixer and the fixing baths for color processing are rapid fixer. I don't know about current prices and availability but you may be able to find made-up rapid fixer at an attractive price. -- Richard Knoppow Los Angeles WB6KBL |
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