[pure-silver] Re: D-76 and variations
- From: titrisol <titrisol@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Mon, 28 Nov 2005 12:57:11 -0800 (PST)
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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