From: Liam Lawless (liam.lawless@blueyonder.co.uk)
Date: 12/02/02-02:47:50 PM Z
My understanding is that *some* sulphiding of image silver takes place in
hypo, due to small particle size and consequent large surface area. But if
conversion of silver to sulphide was complete, or nearly so, I'd expect
subsequent gold toning to give a red image, which it don't.
I'd guess that there's some silver citrate and silver tartrate in the VDB
sensitiser, with free silver nitrate as an accelerator. Silver nitrate is
water-soluble and should wash out with pure water (apart from any compounds
it forms with paper buffering matter, e.g. carbonate), but the citrate &
tartrate would need fixing (though they're very slightly soluble, as I
remember). To test whether any sensitive stuff is present, put a spot of
sepia toner solution in a highlight area. Don't think I've ever tried it,
but I'd bet a millionth of a dollar that the fix is needed.
Liam
-----Original Message-----
From: Judy Seigel [mailto:jseigel@panix.com]
Sent: 02 December 2002 20:05
To: alt-photo-process-l@sask.usask.ca
Subject: Re: toning VDB & kalli - 2 questions
On Mon, 25 Nov 2002 rurmonas@senet.com.au wrote:
> Judy,
>
> I may be wrong here, but my undestanding of VDB was that the thiosulphate
> bath was not a fixing bath, but a simple way of providing sulphur to react
> with the silver. As the silver is much finer than a silver bromide paper,
> the conversion of silver to silver sulphide takes place. This is the same
> as sepia toning and so the resulting print should be quite stable. I
would
> expect Kallitype to be similar.
>
> > What about toning after fixing? Is that effective? It might also alter
> > the color, but then it might not.
>
> If my comments above are correct, then toning after the thiosulphate bath
> would need something that will react with silver sulphide, as well as
> any silver remaining in the print. Thus not all toning baths would be
> suitable.
>
> Perhaps someone will confirm / deny my understanding.
This theory of VDB fixing is one I've never heard -- tho fascinating...
I was hoping someone would have further info or input. How could that be
tested? When my students loved the color of pre-fixed VDB & wanted to
leave print that way, we tested by doubling exposure to unfixed but washed
print -- there was very little change, although the print was overall
flatter than if fixed.
Though what that means re Richard's suggestion I have no idea. I do know
that long fixing (more than a minute in my tests) of VDB starts to bleach
it out, and will ultimately bleach it a lot. What would that say about
whether it is making the silver compound soluble or just sulfiding?
Any chemists listening? any way to test?
Judy
This archive was generated by hypermail 2.1.5 : 01/31/03-09:31:25 AM Z CST