Auteur: PAyral
Date: 23-09-2009 13:19
Méthode pour tester le FO selon Jeffrey Mathias:
The following test can check the viability of your ferric oxalate. It is included in the "Guide to Platinum Palladium Printmaking" on my web site (see link below). It is given here for those who do not wish to acknowledge their free use of the guide with a requested password.
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Note: Testing, as with any handling of Ferric Oxalate, should be carried out in safelight illumination.
To test the Ferric Oxalate solution:
(TEST #1)
Place some Ferric Oxalate solution into a shot glass.
Add a crystal of Potassium Ferricyanide (one or two crystals is plenty to do the job).
Nothing should happen.
If it darkens, the Ferric Oxalate has turned into Ferrous Oxalate and FAILED TEST #1 (do not
consider any orange color from the Potassium Ferricyanide).
If the solution (used in TEST #1) is OLD SOLUTION, make a fresh solution from the stock powder and test again
(TEST #2).
If TEST #2 FAILS and the stock powder is OLD POWDER
(powder was probably not stored correctly or it may have gotten hot), use new powder and test again
(TEST #3).
If TEST #3 FAILS, then the new powder is defective and should be returned to the vender for replacement.
If TEST #3 PASSES, new solution and stock powder are OK.
If TEST #2 FAILS and the stock powder is NEW POWDER, then the powder is defective and should be returned to the vender for replacement.
If TEST #2 PASSES, new solution and stock power are OK.
If the solution (used in TEST #1) is NEW SOLUTION, then the stock powder is bad.
If the stock powder is OLD POWDER, then it has probably been stored incorrectly.
If the stock powder is NEW POWDER, then the powder is defective and should be returned to the vender for replacement.
If nothing happens, continue with TEST.
Place shot glass with Solution in UV light. It should turn deep indigo blue.
If the solution does not turn a deep indigo blue, then the Ferric Oxalate is bad.
If this is a NEW SOLUTION from a NEW POWDER, first try adding some more Potassium Ferricyanide. If there is still a failure to turn blue and the Potassium Ferricyanide is good, then the powder is not Ferric Oxalate.
Return the powder to the vender for replacement. (If this happens again, find a new vender.)
If this is a NEW SOLUTION from an OLD POWDER (that has worked before), then somehow the solution was made incorrectly. Make a new solution from the old power and re-test.
If this is an OLD SOLUTION from an OLD POWDER (that have both worked before), then the Potassium Ferricyanide must be bad. (This is unlikely, but there is no other reason.)
When the solution turns dark blue only under the UV light, then the TEST has PASSED.
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This test is extremely simple and easy and does ferret out most detrimental scenarios. Then making a print from a reference negative to compare with previous results can document consistency. A difference I have been recently studying is that not all sources of ferric oxalate are the same or pure causing the necessity to mix the solutions at different strengths. I have also found that measurements such as that of specific gravity (as suggested by Dick Stevens) cannot provide accurate information as to the content of a ferric oxalate solution because of unknown influences of unknown impurities.
As to some of your other concerns: if one can make six prints, one each month for six months, that are for the most part identical, then they have a good procedure and control of the process. (At times one may even lessen control for desired results.)
--
Jeffrey D. Mathias
http://home.att.net/~jeffrey.d.mathias/
PAyral
http://pagesperso-orange.fr/payral
http://www.apug.org/forums/portfolios.php?u=2668
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