RichardYes, I'm assuming that no significant amount of hypo is clinging to the film emulsion. That is the base assumption for diffusion washing to work. If that is not correct, I'm in trouble.
I should mention that I have the facilities at work to conduct a methelen-blue test, and had it done to verify the test result of the HT-1 test. I gave them a sample of various known concentrations, and they used that to calibrate the test. The results were very promising for HT-1. When HT-1 showed less <=1 mg/l, methelene-blue returned a result of less than 15 mg/m^2. So, there is good correlation.
I don't understand why you keep bringing up the silver nitrate test. It is not even recommended for film testing, or is it? How can it be better? What am I missing? Remember, we are talking about film (not paper) testing.
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 24, 2009, at 01:48, Richard Knoppow wrote:
----- Original Message ----- From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx >To: <pure-silver@xxxxxxxxxxxxx> Sent: Monday, November 23, 2009 9:19 AM Subject: [pure-silver] Re: Mystery Hypo TestYou are assuming that there is no hypo bonded to the gelatin or image silver. Where acid hypo has been used this is possible. Binding is less of a problem for film than for fiber paper where hypo can be bound up in the baryta layer or in the fiber structure of the support. The permanganate test was discontinued because it was simply not effective. The silver nitrate test is better. I will see if I can come up with some citations.Richard I'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 bequantified on clear film. Consequently, HT-2 is not a good replacementfor HT-1. I also think that HT-1 accuracy is underrated. Its application is usually published the same way you described it, with limitedaccuracy, 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 equilibriumbetween film and wash water is reached. In other words, at that point, the thiosulfate concentration of the wash water is the same as that ofthe film emulsion. This way, I can detect down to 1 mg/l of hypo with HT-1, which issufficient, because a typical 35mm or 120 roll film has a surface areaof 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.-- 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.
