[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
> 
> 
> 
>
========================================================================
> =====================================
> 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.
> 



                
__________________________________ 
Yahoo! Music Unlimited 
Access over 1 million songs. Try it free. 
http://music.yahoo.com/unlimited/
=============================================================================================================
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.

Other related posts: