I've used Kodak's indicator stop bath for years which of course lets you know when it's had enough. I'm using their 28% Acetic acid now and am wondering if there is a way of testing it for exhaustion. (yes, I know its cheap so why not just make it fresh more often. I hate tossing anything out that still works)

-- Harv Jenkins (hjenkins@prcn.org), December 10, 2001

Answers

According to Ansel, well before the indicator starts indicating the bath is exhausted and shouldn't be used. His method for testing the stop has always worked for me. Get your hands slimy in the alkaline developer and see how quickly the stop bath cuts it. It should be nearly instantaneous.

-- Ed Buffaloe (edb@unblinkingeye.com), December 10, 2001.

Whenever my developer is exhausted (or I am ready to pour it down the drain), I first pour the stop bath into the developer tray. The resulting discharge should have less environmental impact on the waste water system than disposing of them at separate times. It also has the added benefit of decreasing the likelihood of developer stains in my sink. You should be able to increase the stop bath dilution a little bit if you dispose the stop bath tray with each tray of developer.

-- Michael Feldman (mfeldman@qwest.net), December 11, 2001.

You could use some pH indicator papers. These are available in little books of about 25 strips from chemical supply houses. You'd want a narrow range indicator paper for pH 4 to 9 (say). When the paper indicates that the stop bath is approaching pH 6, then it's time to renew it.
A more direct method to tell if the stop bath is any good is by the look and feel of it. If you dip your thumb and finger in the bath and rub them together, a fresh stop bath feels slightly sticky. A used bath will feel slimy and slippery, and if it has the slightest brown tint to it, then it's time to chuck it.

-- Pete Andrews (p.l.andrews@bham.ac.uk), December 11, 2001.