----- Original Message ----- From: "Gene Johnson" <genej2@xxxxxxx> To: <pure-silver@xxxxxxxxxxxxx> Sent: Thursday, February 17, 2005 7:40 AM Subject: [pure-silver] baking soda as wash aid >I saw on the Summitek site a suggestion for using Baking >soda in the print wash water as a wash aid. Any thoughts >on this? Economical and low tox if it works well. > It may be alkaline enough to work the way a carbonate bath does but does not have the ion exchange properties of sulfite. I don't have the Kodak paper on wash aid readily available at the moment but I think sodium bicarbonate was among the salts they tested. The idea of the Kodak wash aid is that it is alkaline enough to obtain optimum washing conditions but not so alkaline as to remove the hardening from alum plus the sulfite is effective in displacing thiosulfate and fixer reaction ions. A simple alkaline bath, such as the carbonate bath recommended by Agfa, will adjust the pH of the gelatin to a value where it no longer binds thiosulfate and where the "mordanting" action of alum hardener is eliminated, however, it undoes the hardening and has no ion exchange effect. Kodak Hypo Clearing Agent is essentially a 2% solution of Sodium Sulfite buffered to neutral with Sodium bisulfite. It also includes two sequestering agents to prevent a sludge forming from minerals in the water when it is re-used. Many years before the wash aid was developed Kodak Labs did a test on various alkalies as wash aides. The one they found most effective was Ammonium carbonate, perhaps because it washes out fast itself. This is mainly of historical interest because of the later research showing that buffered sulfite was much superior to any alkali bath. --- 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.