Re: An exchange with Mike Ware (on Argyrotype)

From: roger kockaerts <permadocument@yahoo.com>
Subject: Re: An exchange with Mike Ware (on Argyrotype)
Date: Sun, 26 Mar 2006 21:20:39 +0200 (CEST)

> In silver printing we generally fight a war against trace
> thiosulfate and have some efficient quantitative measuring
> techniques at our disposal. Nothing of the sort exists (at my
> knowledge) to do the same with the iron processes. It would be
> convenient if our chemical geniuses could come up with a practical
> way to measure tolerable residual iron.

There are some tests I suggested on this list in the past. The
simplest one is to use thiocyanate, which binds to Fe(III) to make
blood-like red color.

/lists/alt-photo-process/2004/mar04/0350.htm

Thiocyanate is reactive with Fe(III) but not Fe(II). To test for the
presense of either form of iron, Fe(II) should be oxidized by air or
peroxide before testing. (Whether you need to do this or not depends
on what form of iron is present in the formula, but probably
unnecessary in many practical situations.)

Another method uses 1,10-phenanthroline or 2,2'-bipyridine. These
agents are directly reactive with Fe(II) and not Fe(III), and make
blood-like red color. Similarly, Fe(III) must be reduced first, to
test for the presence of iron in either form.

It's probably easier to go with thiocyanate test.
Received on Sun Mar 26 13:48:27 2006