D-76 is very poorly buffered thus even a small amount of oxidation is enough to raise the pH significantly. There is a variant which contains sodium carbonate and sodium metabisulfite which creates a carbonate/bicarbonate buffer. Packaged D-76 probably contains some sequestering agent which would help preserve it. During the oxidation of hydroquinone, hydroquinone monosulfonate ion is produced. This is also a developing agent although it is not as active as hydroquinone itself. Potassium hydroquinone monosulfonate is Kodak's Balanced Developing Agent which sometimes appears in their formulas. Sodium carbonate solutions will absorb CO2 from the air to form bicarbonate ion. But not enough to effect paper developers. -----Original Message----- From: pure-silver-bounce@xxxxxxxxxxxxx [mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of John Black Sent: Monday, November 28, 2005 1:26 PM To: pure-silver@xxxxxxxxxxxxx Subject: [pure-silver] Re: D-76 and variations The problem with the rise in pH of D-76 with time is due to the oxidation of hydroquinone. This is a fairly complex reaction in which OH- ions are produced. It has nothing to due with either carbonates or borax. Oh.... other than buffering it, what was done about the pH problem with storage? If hydroquinone oxidizes, is it still photographically active? I could have sworn that there was an old formula or variation of D76 that had carbonate in it. Pure Na carbonate solutions are quite alkaline but not of a long term pH stability. There seems to be an interaction between CO2 in the air and carbonate ion, or so I've been told. In paper developers that use carbonate, a rise in pH is not noticeable activitywise. JB ======================================================================== ===================================== 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. ============================================================================================================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.