RichardI'm looking for a more reliable hypo test for films without having to go to methylene blue. As far as I know, HT-2 is very useful for paper but virtually useless for films, because the stain cannot be quantified on clear film. Consequently, HT-2 is not a good replacement for HT-1.
I also think that HT-1 accuracy is underrated. Its application is usually published the same way you described it, with limited accuracy, because it tests the wash water and not the emulsion itself. However, when modifying the test slightly, it can deliver amazing sensitivity. I modified the standard test procedure as follows: I immerse a fully washed film into a 0.5-liter bath of distilled water. With light agitation, let it soak for 6-10 minutes, after which, the residual thiosulfate is fully diffused and an equilibrium between film and wash water is reached. In other words, at that point, the thiosulfate concentration of the wash water is the same as that of the film emulsion.
This way, I can detect down to 1 mg/l of hypo with HT-1, which is sufficient, because a typical 35mm or 120 roll film has a surface area of roughly 80 in^2 or 0.05 m^2. If it has been washed to the archival standard of 15 mg/m^2, and the residual thiosulfate of one roll film (0.75 mg) is fully diffused in 0.5 liter wash water, the thiosulfate concentration of the water must be at or below 1.5 mg/l.
I was hoping to have found an even more accurate test with this Crabtree formula, but it may not work.
Regards Ralph W. Lambrecht http://www.darkroomagic.comThis electronic message contains information that is confidential, legally privileged or otherwise protected from disclosure. This information is intended for the use of the addressee only. If you are not the intended recipient, you are hereby notified that any disclosure, copying, distribution, printing or any other use of, or any action in reliance on, the contents of this electronic message is strictly prohibited. If you have received this communication in error, please notify the sender and destroy the original message immediately.
P don't print this e-mail unless you really have to On Nov 23, 2009, at 00:34, Richard Knoppow wrote:
----- Original Message ----- From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx >To: <pure-silver@xxxxxxxxxxxxx> Sent: Sunday, November 22, 2009 2:35 PM Subject: [pure-silver] Re: Mystery Hypo TestThe first residual hypo test was one using potassium permanganate to test water run off from the print or negative. The problem was that the run off water could be relatively free of hypo while excessive hypo was bonded to the emulsion and support. It was not a satisfactory test despite being published for years. Its replacement was the silver nitrate test. This is practical and sensitive enough to determine when material has been washed down to archival levels. The methylene blue test is the newest but is mostly for specialized uses such as research and microfilm since it is rather complex. HT-1 and HT-1a are the permanganate test. The 1940 edition of _Photographic Facts and Formulas_ also contains the mercuric chloride test attributed to Crabtree and Ross but without a citation. I think this is not a very satisfactory test and evidently was not used for long. This does confirm my first impression that it was a very old test. The most satisfactory test for general use is the silver nitrate test Kodak HT-2. Again, HT-2 can be made quantitative by fixing the stain. I will have to find the method. I doubt seriously if HT-1 works better or is more sensitive.Richard That's good, but keep in mind, just as the book suggests, I'm interested in this formula as a substitute for HT-1 not HT-2. My goalis to have a better hypo test for film without going to methylene- blue.Regards Ralph W. Lambrecht http://www.darkroomagic.com-- 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.
