[pure-silver] Re: D-76 and ID-11
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: "Pure-Silver Free" <pure-silver@xxxxxxxxxxxxx>
- Date: Tue, 6 Nov 2007 13:53:48 -0800
----- Original Message -----
From: "Shannon Stoney" <shannonstoney@xxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, November 06, 2007 11:57 AM
Subject: [pure-silver] D-76 and ID-11
This brings up a related question. ID-11 and D-76 are
often said to be the same developer formula. But Ilford
gives different times for ID-11 and D-76. For example,
for HP5+, Ilford suggests a time of 13 min for ID-11 1+1,
but 11 minutes for the same dilution of D-76. Weirdly,
for FP4+, it suggests a longer time for D-76 than for
ID-11. That suggests to me that they aren't exactly the
same formula.
--shannon
The published formulas are identical. Every manufacturer
of film or chemistry had some version of D-76. However, the
packaged formulas are not the same. Kodak D-76 is a buffered
version, similar to the published formula D-76d. The
buffering is to eliminate a problem discovered shortly after
the release of the D-76 formula in 1926. When stored there
is a slow reaction between the hydroquinone and sulfite
which results in a small amount of sodium hydroxide being
produced. Over a period of weeks this raises the pH and thus
the activity of the developer. According the the data in a
scientific paper published by Kodak in 1929 the activity of
unused developer increases to the point where the time
required to reach a given gamma (contrast) is nearly halved
after a month. The buffered type developer has pretty much
constant activity. I don't know what Ilford does about this,
if anything, but they buffer Microphen which is a Phenidone
developer based on D-76. Both packaged formulae also contain
other ingredients, which do not show up on the MSDS, for
instance sequestering agents to deal with dissolved minerals
in the water and also perhaps a silver sequestering agent to
reduce the slight fogging this type of developer tends to
produce when used fresh. BTW, both Microdol-X and Perceptol
also include such agents.
Now, the time differences may be the result of somewhat
test conditions. Also, Ilford uses a different agitation
method than Kodak for small tanks. There are other factors
too so the difference may not be the strictly the activity
of the developer.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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