[pure-silver] Re: D-76 and variations

I was of the understanding that the packaged version was similar to
D-76d but contained half the amounts of borax and boric acid.  There are
many ways to create the necessary buffer, the use of Kodalk would just
require more boric acid.

-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of titrisol
Sent: Monday, November 28, 2005 3:57 PM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: D-76 and variations


I always thought packaged D76 used Metaborate (Kodalk) to keep the
buffering power

--- "Koch, Gerald" <gkoch02@xxxxxxxxxx> wrote:

> 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
> 
> 
> 
>
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