[pure-silver] Re: odd neg
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Sat, 14 Nov 2009 07:04:22 -0800
----- Original Message -----
From: "Eric Nelson" <emanmb@xxxxxxxxx>
To: "pure silver" <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, November 13, 2009 9:16 PM
Subject: [pure-silver] odd neg
I was asked to push a delta 100 4x5 neg 2 stops so I opted
for t-max developer @75 for 7 mins.
This is the odd looking result.
http://img254.imageshack.us/img254/6230/wtfkb.jpg
Now I suppose the thing will print fine but what is that
odd color there? Tmax RS is supposed to prevent that
chromatic whatchamacallit but there were no times for RS
in the Ilford literature and I was already having to give
my best guess as to the time.
thanks
Eric
Supposedly T-Max RS has a silver sequestering agent in
it to prevent dichroic fog. Not all developers produce
dichroic fog but T-Max, without the RS is not recommended by
Kodak for sheet film for this reason. I am not sure how
close the formulas are otherwise, my suspicion is that there
are more differences. The RS means Replenis System because
the developer is also its own replenisher. Again, this is a
bigger difference than just a dichroic fog preventer.
Its possible youre negatives have dichroic fog, I can't
really tell from the scan. Dichroic fog is a coating of
colloidal silver on the surface of the negative. It appears
greenish or bluish by reflected light and yellowish by
transmitted light. It can have an oil-slick appearance by
reflected light. Dichroic fog can be removed by using a mild
silver solvent. Kodak's current recommendation is to use
film strength rapid fixer with about 15grams/liter of citric
acid added. Ammonium thiosulfate fixer, when acid, is a mild
solvent for metallic silver and the citric acid acts as a
sequestering agent to prevent the dissolved silver from
being re-deposited on the film.
BTW, this silver solvent action is the reason rapid
fixer can cause some bleaching of paper if fixing is carried
on too long. Its also the reason that a weaker dilution is
recommended for paper. The bleaching action exists only when
the fixing bath is sufficiently acid, neutral rapid fixer
does not bleach.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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