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<p>[QUOTE="dougsmit, post: 3768549, member: 19463"]When we met I could have given you a bunch of it but no more. Sodium thiosulphate was common photo fixer. It dissolved unexposed and undeveloped silver halides (chloride, bromide etc.) leaving a more permanent image we called a photograph. That material would dissolve horn silver. Chloride would darken when exposed to light. Early photos faded or actually darkened to black until it was discovered that thiosulphate would dissolve unexposed halides and leave the darkened ones. </p><p><br /></p><p>Later, photo technology evolved and added a substance that hardened the film that reduced the effectiveness on coins. Then they invented what was called 'Rapid fixer' that was better for photography but did nothing for coins. Toward the end of my time in the Army, it was getting hard to find the old style fixer. In 2000, I bought a digital camera and never again owned any fixer. I'm sure you can buy the stuff in reagent purity today but back then the stuff was cheap as dirt in good enough for photo and coin quality. Well used photo fixer could be used to silver plate copper pennies. This was long before people decided that they should recover the silver from used photo chemicals. Another useful chemical for coin cleaning as I recall was called 'Farmer's Reducer'. It was used to lighten over exposed negatives to make them usable. It was a set of two baths Potassium fericyanide(?) and thiosulphate. I have forgotten when I used both and when I used just the fixer. </p><p><br /></p><p>All I remember about the practical use is that removing an evil (horn silver or other) was no guarantee that what was under the stuff was any better looking than it was to start.[/QUOTE]</p><p><br /></p>
[QUOTE="dougsmit, post: 3768549, member: 19463"]When we met I could have given you a bunch of it but no more. Sodium thiosulphate was common photo fixer. It dissolved unexposed and undeveloped silver halides (chloride, bromide etc.) leaving a more permanent image we called a photograph. That material would dissolve horn silver. Chloride would darken when exposed to light. Early photos faded or actually darkened to black until it was discovered that thiosulphate would dissolve unexposed halides and leave the darkened ones. Later, photo technology evolved and added a substance that hardened the film that reduced the effectiveness on coins. Then they invented what was called 'Rapid fixer' that was better for photography but did nothing for coins. Toward the end of my time in the Army, it was getting hard to find the old style fixer. In 2000, I bought a digital camera and never again owned any fixer. I'm sure you can buy the stuff in reagent purity today but back then the stuff was cheap as dirt in good enough for photo and coin quality. Well used photo fixer could be used to silver plate copper pennies. This was long before people decided that they should recover the silver from used photo chemicals. Another useful chemical for coin cleaning as I recall was called 'Farmer's Reducer'. It was used to lighten over exposed negatives to make them usable. It was a set of two baths Potassium fericyanide(?) and thiosulphate. I have forgotten when I used both and when I used just the fixer. All I remember about the practical use is that removing an evil (horn silver or other) was no guarantee that what was under the stuff was any better looking than it was to start.[/QUOTE]
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