From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 12/16/02-12:37:12 AM Z
On Mon, 16 Dec 2002 00:13:48 -0500 (EST) Judy Seigel <jseigel@panix.com>
wrote:
>
>
> On Sun, 15 Dec 2002, Sandy King wrote:
>
> > It is my understanding that Kodak currently
> buffers their packaged
> > D76 developer so, assuming that your solution
> was mixed from a
> > prepared package it would not have increased
> in alkalinity over this
> > period of time.
>
> Well this was some time ago, as I have not used
> D-76 recently... Reading
> this discussion I theorize that as the solution
> got weaker with age, the
> pH picked up, so net activity remained the
> same. (Would that we could say
> the same.)
>
> Meanwhile, I note that Sandy and others are
> mentioning pH -- how are
> you/they measuring it? I found the strips
> (hyperion? or like that)
> unsatisfactory, not precise, aged quickly, etc.
> Bought a digital poker
> type instrument, but it was worse,
> inconsistent, slow & generally wiggy.
> Is there anything short of major outlay that
> works well?
>
> J.
>
>
>
> >
> > That would not be true, however, if you mixed
> the D76 from scratch to
> > the original formula.
> >
> > Sandy King
> >
> >
> >
> >
>
The current packaged D-76 _is_ the buffered version. See the MSDS for more.
The rising activity effect was discovered shortly after the introduction of
D-76 in 1926. In 1929 a paper was published by Carlton and Crabtree, of Kodak
Labs, discussing the effect. They made extensive measurements and discovered
that the ph of stored solution rose slowly over time. The rise was sufficient
to about halve the time required to achieve a given gamma after about a month.
The paper describes over thirty variations of D-76, including the buffered
version. While the cause of the rise in pH was not determined at the time it
is now known to be a complex reaction between the Hydroquinone and the
sulfite. This produces some hydroxide and also some very active reaction
products of the hydroquinone.
Evidently, there is some similar effect in all hydroquinone containing
developers.
Micheal Gudzinowicz posted a rather complete analysis of the reactions in
the rec.photo.darkroom group. A Google search will find them.
I am not at home so don't have the citation for the Carlton and Crabtree
paper at hand, but it was published in one of the 1929 numbers of the
_Transactions of the Society of Motion Picture Engineers_
FWIW, here are the formulas for the original and buffered versions of D-76
Kodak D-76
Water, at 125F 750.0 ml
Metol 2.0 grams
Sodium Sulfite, dessicated 100.0 grams
Hydroquinone 5.0 grams
Borax, granulated 2.0 grams
Water to make 1.0 liter
Kodak D-76d Buffered Borax Developer
Water, at 125F 750.0 ml
Metol 2.0 grams
Sodium Sulfite, dessicated 100.0 grams
Hydroquinone 5.0 grams
Borax, granulated 8.0 grams
Boric Acid 8.0 grams
Water to Make 1.0 liter
When made up with equal amounts of Borax and Boric Acid, as above, the
activity is the same as _fresh_ standard D-76.
A note: it was asked about mixing at elevated temperatures. There are two
reasons for avoiding higher temperatures than specified by Kodak, 1, there may
be a tendency for some of the components to decompose at higher temperatures;
2, oxidation may take place at a faster rate.
Because Metol will not dissolve in high concentrations of Sulfite it must be
dissolved first. In order to minimise oxidation use water which has been
boiled and allowed to cool while standing. Boiling drives off the dissolved
air in the water. It is also helpful to dissolve about 15 grams/liter of
Sodium Sulfite first. This is not enough to interfere with the solution of the
Metol but is enough to scavenge remaining oxygen in the water.
Richard Knoppow
dickburk@ix.netcom.com
Los Angeles, CA, USA
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