Aluminum chloride

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Olympusman
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Joined: Sun Jan 15, 2012 12:31 pm

Aluminum chloride

Post by Olympusman »

This is photographic fixer hardener. What it does it contracts the gelatin in a black white film emulsion. Way back in the early eighties, one of my photography professors in college asked me if it thought 120 Tri-x was losing its sharpness. After a few conversations on this topic I learned that he had found he could buy a fifdty pound bag of Sodium thiosulfate from Eastman Chemical for about fifty dollars, and that was what he was using for his film and paper fixer. The lack of sharpness was that he was not adding Alum (Aluminum chloride) to his fixer, that was needed to harden the emulsion. With the high temperature of tap water in Phoenix, Arizona, without the hardener (Alum), the emulsion swelled, and when it dried, the result was grain clumping, resulting in a lack of accutance in the grain structure. Sincen then, I have learned, you can prepare rinse water to the desirable temperature and effectively wash your film in six changes of water, withoutr having to run the reels under the tap.
Aluminum chloride does cross-polarize, but the crystal structure comes across better with featherd darkfield.
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Michael Reese Much FRMS EMS Bethlehem, Pennsylvania, USA

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