[pure-silver] Re: Mystery Hypo Test


----- Original Message ----- From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Sunday, November 22, 2009 1:33 PM
Subject: [pure-silver] Mystery Hypo Test


Richard mentioned this book a few times: 'Photographic Facts and Formulas'. I was lucky enough to get a copy of the 1975 edition on
Amazon for a song. Good book!

On page 156, it lists a nameless formula of a hypo test for film, apparently far more sensitive than Kodak's HT-1a, which is listed on
the previous page.

mercuric chloride   25 g
potassium bromide   25 g
water to make   1000 ml

The book goes on to explain that it was suggested by Crabtree and Ross (big names) and gives a detailed description of its application.

Has anybody ever used this? Why does it not have a name? Is it a best-
kept secret because of its first ingredient?





Regards



Ralph W. Lambrecht

http://www.darkroomagic.com

The standard test for hypo is the methylene blue test. This is more sensitive than the silver nitrate test and can be quantitative. I don't remember where the details are at the moment but think they are in an ISO standard. I think I know about the test above but don't remember much about it. Anything with a mercury compound in it is worth avoiding. Not only is mercuric chloride hard to obtain it is an extremely toxic substance. I think this test is a pretty old one. The silver nitrate test can also be made quantitative by fixing the stain in a sodium chloride solution and measuring the density in comparison to stains on similar material made with known amounts of hypo. Again, I can't remember where the procedure is detailed. Possibly in Grant Haist's book but my copy is stored away. I will do some research on this, youv'e got my curiousity piqued.

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



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