----- 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 onAmazon 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 onthe previous page. mercuric chloride 25 g potassium bromide 25 g water to make 1000 mlThe 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 ============================================================================================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there.