rurmonas@senet.com.au
Date: 12/06/02-05:11:02 AM Z
Quoting Liam Lawless <liam.lawless@blueyonder.co.uk>:
> My guess is that insoluble silver salts are not present in the sensitiser,
> but form on contact with buffered papers and that, maybe, you'd get away
> with just washing VDBs on unbuffered paper. But maybe not, too, because
> some organic, insoluble silver salts might form with the paper matter
> itself. One way to test that would be to repeat your test on a synthetic
> paper - I had some once, but it was such horrible stuff I threw it away. I
> tried coating VDB on plastic, but couldn't. I can't do a conclusive test,
> therefore, but do have an unbuffered paper here, Atlantis Silversafe, and
> some Arches Aquarelle which I know is heavily buffered with carbonate
I can see things two ways:
1) Insoluble silver salt
2) Low solubility / mechanical "trapping" effects, either in the paper
fibres, or ferric compounds harden gelatine (and may affect other sizes)
thus any VDB solution which soaks into the sizing could be slow to wash
out due to the size being hardened.
Either way we can say that a practical washing time will not remove all the
silver, and so we need to fix.
> OK, the results are in (some 2 hours later): I used a thiourea sepia toner
> (10 g thiourea + 10 g sod. hydroxide in 1 litre), and toning produced bad
> staining on both papers when they had been washed 10 minutes but not fixed.
> Staining was a little less on the unbuffered. This suggests to me that
> buffered paper is one reason why fixing is needed, but not the most
> important one. The formation of insoluble organic silver compounds on the
> paper is another explanation, but it strikes me that there could be another:
> residual iron, forming ferrous sulphide on toning. I seem to remember
> hearing/reading somewhere that hypo gets rid of iron, but can't remember
> where or say if it's true.
>
> 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
> 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.
Oh great now we have opened a pandora's box. I tried putting a fixed VDB
into thiourea toner (without bleaching step). As you said a colder tone
and I noted better seperation of shaddow details. So tried a fixed
VBD in alakali and acid with no obvious effect (this was this morning
before work, so I did not have time to dry prints).
In some recent cyanotype testing I noted that if paper is coated with
just FAC (no ferricyanide) and exposed and washed there is a "dirty
yellow" image formed. So tried this in acid, alkali, and fixer. It
is not readily soluble in any of these. So it is possible that some
iron can find its way into the final VDB image (after fixing etc. etc.).
Tried this FAC image in the thiourea toner, but no effect. So this is
not the direct cause, but still allows the possibility of iron compounds
in the final image.
So now I am thinking about removing the silver image to see if there is
anything "underneath" the silver image. So I have a VDB soaking in
film strength fixer, as well as a FAC only image, a cyano image (to see
what effects happen to it), and a silver gelatine print (as a control
for silver removal). There were still good images on all samples after
1 hour, so I have left those to soak during the day.
I will let the list know the outcome of this.
The game is afoot.
Richard
--- Richard Urmonas rurmonas@senet.com.au ------------------------------------------------- This mail sent through SE Net Webmail http://webmail.senet.com.au
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