[pure-silver] Re: Mystery Hypo Test

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <pure-silver@xxxxxxxxxxxxx>
  • Date: Sun, 22 Nov 2009 14:09:10 -0800

----- 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?


Ralph W. Lambrecht


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

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