[alt-photo] Re: Stoichiometry for the nonscientist

Loris Medici mail at loris.medici.name
Tue Aug 3 14:15:48 GMT 2010

Thanks for the clarification Eric. So it's more common to use a slightly
acid developer then...

OTOH: (Please don't take them as nitpicking - this is just what comes in to
my mind...)
- I would never print on buffered paper. And if I definitely have to use a
buffered paper, I would neutralize/acidify it beforehand. I don't believe
buffered papers (at time of printing) will give nice results with the
process - that's not my experience with any of the iron processes...
- The sensitizer itself is pretty acid (around pH 3 or 4 - if I'm not
mistaking), therefore, each processed print will actually slightly increase
the acidity of the developer - which is something to consider when re-using
the developer indefinitely (or for a long time - by filtering out debris and
adding fresh developer to compensate the losses), as most do...


P.S. Agree that it's better / more convenient to purchase potassium oxalate
directly, instead of compounding it yourself. (My approach was that it would
indeed make a nice example for the chemistry stuff we were discussing
lately...) OTOH, if I were using develop out pt/pd myself - and also
determined to use potassium oxalate; since there are many other alternative
developers... - I would definitely have to compound it myself, since we
can't find potassium oxalate (for reasonable prices) here in Turkey...

P.S.2. Etienne, thanks for KOH tip, looks much more convenient than the
fizzling K2CO3. (Except for the exotermic dissolution reaction, one has to
use start with very cold water I presume...)

-----Original Message-----
From: alt-photo-process-list-bounces at lists.altphotolist.org On Behalf Of EJ
Sent: Tuesday, August 03, 2010 4:42 PM
To: 'The alternative photographic processes mailing list'
Subject: [alt-photo] Re: Stoichiometry for the nonscientist

As far as where to stop with the mixing, I do not agree with Loris that many
go to pH7 with this. I keep my solution slightly acid, around pH5 and allow
for a little excess oxalic acid to help keep it that way after several
sheets of buffered papers is run through it. 

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