[alt-photo] Re: dilution of pt/pd

[Terry King]

Loris  


I am afraid that the evidence does not support your contentions.



In everyday practice of develop out platinum printing, using the dilutions I have already cited,  there is no difference between ammonium ferric oxalate and ferric oxalate.


In fact for many years, as I had never experienced 'solarisation' with platinum printing using ferric oxalate, I wondered what people were talking about. What did make a difference was using  precious metal solutions that were too weak or papers which were highly buffered when there had been no pre-soak in oxalic acid..


As I have made ferric oxalate as an exercise on workshops from year to year, I can tell you from the evidence of having ferric oxalate of different vintages, that ferric oxalate in solution loses in speed by about a third of a stop a year.   Ferric oxalate, kept in brown bottles, as  much as five years old is still perfectly usable given the appropriate exposure.  I suggest that you correct your notes to take account of this evidence. 


It is easy to dissolve ferric oxalate, just keep it in a warm water bath and stir from time to time. There are simple tasks in cookery which are more complicated.


I calibrate my negatives and have had no problems with ferric oxalate using different sources of supply,( apart from having to add oxalic acid), and solutions made in class using different methods.


There seems to be far too much 'research' to solve problems which do not exist. That has been true over the history of photography from 'The Silver Sunbeam' to Mike Ware.


Terry







-----Original Message-----
From: Loris Medici <mail at loris.medici.name>
To: The alternative photographic processes mailing list <alt-photo-process-list at lists.altphotolist.org>
Sent: Sat, 24 Jul 2010 12:16
Subject: [alt-photo] Re: dilution of pt/pd


Terry,

2010/7/24 Terry King <terryaking at aol.com>:
> ...
> The results of our tests show that it makes no difference whether you use 
ammonium ferric oxalate or ferric oxalate in making
> platinum prints. These and other circumstances have led myself and others, 
including those with great chemical expertise, to
> doubt Dr Ware's chemistry even if that is lese majesty.
> ...

In fact, there are considerable differences between FO and AFO:
1. FO gives a whisper image and needs development, whereas AFO gives
full print out (unless the wheater is excessively dry) and doesn't
need a developer.
2. You almost never experience solarization with AFO + pure Pd metal
soln. (because of self-masking), whereas solarization is more a
problem with FO sensitizer when using a metal solution with just Pd.
3. AFO sensitizer never goes bad, whereas you have to pay attention to
use relatively fresh FO (not older than 3 months, max. 6 months... And
there are practitioners who prefer to mix fresh soln. in small amnts.
beforehand / per ), in order to avoid fog. Or, adulterate FO after
some time, in order to convert Fe(II) to Fe(III) - which is a PIA!
3 1/2. Related to 3, dissolving FO is even a greater PIA, it's a
relatively slow and complicated process (=hours, heating etc.) whereas
AFO dissolves in a snap...
4. With AFO, you always get the same compound regardless the
production batch and/or supplier, whereas the composition of FO may
change from batch to batch and/or from supplier to supplier. (Which is
something to consider, if you opt to carefully / painstakingly
calibrate your negatives to the process...)
5. And more... (Which I may have forgotten to bring into consideration.)

IMPORTANT / N.B.: All of the above wasn't ment say "AFO is better than
FO", or the opposite. The sole purpose was to list the principal
differences between the two ferric salts we use in pt/pd printing...
Each practitioner has their own "well considered" preference for the
ferric salt they use, and no one is criticizing and/or doubting those
personal preferences here!

Regards,
Loris.
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