From: Liam Lawless (liam.lawless@blueyonder.co.uk)
Date: 12/05/02-06:45:51 PM Z
Judy,
I beleve that the majority of art papers are now buffered, although they're
not always described as such. Indeed, "permanent" papers should contain
alkaline reserves according to the ANSI Z39 (US) Permanent Paper Standard.
Anything labelled acid free and not specifically designated unbuffered is
probably buffered. When did buffering start? Don't know, but according to
Silvie Turner (The Book of Fine Paper): "A move to make certain grades of
machinemade papers (mostly artists' and book papers) acid free is due partly
to pressure put on manufacturers by librarians, particularly in the USA."
pH pens? Don't know - never had one, never seen one. But probably yes -
try damping the paper (pure water!) first if it doesn't work dry, or soak a
piece and test the drippings.
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."
Traditional Pt/Pd is similar to VDB, in that exposure produces a weak image
that "pops" in the developer. On this, KOL says: "On exposure to light the
ferric salts are reduced to the ferrous state. When the paper is placed in
a potassium oxalate developer, the new ferrous salts are dissolved and in
turn reduce the platinum salts in contact with them to the metallic state.
The print is then cleared in hydrochloric acid to eliminate the ferric salts
remaining in the paper."
Ferric ammonium citrate, used by VDB & cyano, isn't quite the same thing as
ferric oxalate, used in trad. Pt/Pd, and does not require a clearing
stage... or so we're told!! (scary background music) But I believe the
image-forming mechanism is the same - ferric iron salt becomes ferrous under
UV, reducing some of the silver, ferricyanide or whatever as it does so, but
the bulk of the VDB silver forms when the print is treatd with a solvent for
the ferrous salts, to wit, hypo. (For cyano, the solvent is water and a
stronger print-out is obtained without development.)
Water causes negligible popping of exposed VDB, but is a more effective
developer of f.a. citrate with gold chloride, though there are better ones.
(And for f.a.c./gold prints, separate clearing IS necessary). Bud did
anyone ever try putting a cyanotype straight into hypo, and if so, what
happened?
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.
That's what I think, anyway.
Liam
-----Original Message-----
From: Judy Seigel [mailto:jseigel@panix.com]
Sent: 05 December 2002 08:46
To: alt-photo-process-l@sask.usask.ca
Subject: RE: VDB test results - part 1
On Thu, 5 Dec 2002, Liam Lawless wrote:
> P.S. The scale was several steps shorter with the unbuffered paper
(equals
> a more contrasty print), though whether this is actually due to its lack
of
> buffering I couldn't say, though I suspect it is. And something
Liam, if I read you correctly, you're suggesting that most contemporary
papers are buffered... Can you tell this with a pH pen? Light
Impressions for instance sells one that you can mark the paper with, the
color shows pH -- presumably giving, or suggesting, that info.
I have a bunch of paper about 70 years old -- a Strathmore drawing paper
that was "prewar" (pre world war 2), bought out of a warehouse by NY
Central & put into pads. It's great for cyano and VDB -- and SURELY is
unbuffered. (When did they start doing that??) If there's some simple test
I can do on that with cyano, let me know... But I mention that during all
this discussion I kept thinking that one hallmark of fixing VDB is
ALWAYS, on every paper, the INSTANT you put it in the fixer, even old,
weak, contaminated fixer, it simply POPS into a MUCH darker color.
That's the very dilute sodium thio in water.... What if anything does that
say about whether it's sulfiding or fixing?
J.
> interesting: when a fixed and (fairly briefly) washed VDB was put in sepia
> toner (as above), the shadows darkened quite quickly and the image tone
> gradually became cooler. No bleach was used before the toner.
>
>
> Liam
>
&c.
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