From: Liam Lawless (liam.lawless@blueyonder.co.uk)
Date: 12/05/02-10:39:47 PM Z
Richard,
We've come a long way from the original question, but...
There may be several f.a.c. processes that develop in water, and VDB is one
of them - water may not be a very good developer here, but there is a slight
change in the wash. But I doubt if "exposed f.a.c." exists in the same form
in different processes - more likely it enters into compounds with the
silver, ferricyanide, gold or whatever, which no doubt have different
solubilities, hence the efficacy of different developers. If it was the
same substance, water ought to develop VDB as well as cyano.
My point about hypo and cyano was that hypo might be a more efficient
developer (i.e. giving a stronger image) that has been overlooked because
water works so well. On the other hand, maybe not - I don't know.
Alkaline thiourea does not have much effect on "normal" silver prints
(though it will tone them if allowed enough time), but VDB/kalli, etc.,
present a much greater surface area of silver for it to work on, and this
makes them much more susceptible to all sorts of chemical influences. VDB,
however, can tolerate relatively strong hypo concentrations without ill
effect, and so differs from kalli in that respect. Possibly in other
respects, too. But the fact remains that we've both witnessed VDB change in
alk. thiourea. If we don't believe that's due to silver sulphiding, maybe
we should be checking whether residual iron remains after fixing and forms
ferrous sulphide in the toner. I don't remember who (Ed Buffaloe? Wynn
White?), but I believe someone has checked VDBs for iron and found nothing
to worry about.
I'm quite sure I've printed out f.a.c. and developed with gold chloride, but
my memory isn't what it was (I'm over 40, you know). However, I've just
come back from the kitchen where I developed a dirty yellow f.a.c. image in
ferricyanide and DID get an image in Prussian blue. Two suggestions: on its
own, f.a.c. needs a lot of exposure, on a par with cyanotype, and secondly,
I used strongish solutions (f.a.c. 18%; pot. ferri. about 10%).
And a couple of observations: I only have half a print of a Stouffer showing
the highlight end(having torn the print in half), but it appears to have
printed a very long scale (17 or 18 steps); I'll have to check the shadows
by doing a whole print some time. D-max is lower than for ordinary
cyanotype, and the colour is softer. The other half of the print, the
shadow end, was washed about 2 minutes before development; the dirty yellow
washed off very nearly completely, and produced just the ghost of a blue
image. I don't know if longer washing would have removed it completely. If
you want to try it, the developer must sweep across the whole image: tip one
end of the dish, insert one end of the print and quickly lower the dish,
allowing the "developer" to cover the print quickly and evenly. Otherwise
you'll get streaks.
Yes, Herschel must have been doing positives if developing with
ferrocyanide, but he did a lot of variations, apparently. But I think
you'll find Prussian blue is iron (III) - ferric - ferrocyanide.
Liam
-----Original Message-----
From: rurmonas@senet.com.au [mailto:rurmonas@senet.com.au]
Sent: 06 December 2002 11:51
To: alt-photo-process-l@sask.usask.ca
Subject: RE: VDB test results - part 1
Quoting Liam Lawless <liam.lawless@blueyonder.co.uk>:
> That the image "pops" in hypo is I think explained by the fact that it
makes
> the iron soluble. KOL describes one of Herschel's discoveries: "that on
> exposure to light ferric salts become reduced to the ferrous state, and
that
> the ferrous salts so produced can combine with or in turn reduce other
salts
> to create an image."
I differ here. There are several FAC based processes which develop
in water. This suggests that the ferrous component of exposed FAC is
soluble in water. Hypo is however a silver solvent, so there may
still be some validity to your argument.
> did
> anyone ever try putting a cyanotype straight into hypo, and if so, what
> happened?
A washed cyano. Fixer has no effect (I was experimenting with clearing
paper staining). I have not tried the effect with an unwashed cyano.
I suspect it will develop normally with perhaps some change in tone
due to addition of other chemicals into the prussian blue structure.
> My belief, then, is that hypo is both developer and fixer for VDB, and
that
> the image substance is predominantly silver. Because the silver particles
> are very fine, I expect that a small amount of sulphiding takes place, but
> not much. VDB silver(?) responds to gold toning in much the same way as
the
> silver of a chlorobromidebromide print, not in the way that silver
sulphide
> does on sepia toned prints. And last night a sepia toning solution
produced
> visible change in a VDB print, which I would not expect it to do if the
> image was of silver sulphide already.
However thiourea toner (without bleach) should have minimal reaction
with metallic silver (which is why normally we use a bleaching step).
Of course the fine size of the silver could allow more reaction to take
place. I suspect there is a more to this than a simple silver or silver
sulphide issue.
Richard
--- Richard Urmonas rurmonas@senet.com.au ------------------------------------------------- This mail sent through SE Net Webmail http://webmail.senet.com.au
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