From: Liam Lawless (liam.lawless@blueyonder.co.uk)
Date: 12/04/02-09:38:04 PM Z
Good work, Richard, you've proved an important point. It hadn't even
occurred to me that it needed proving, but if there's a rumour circulating
that VDBs/kallis dont need fixing, well... it has to be squashed.
When you toned, you said that the density produced got less with longer
washing times. Washing removes soluble compounds, not insoluble (unless a
few "loose" crystals on the surface), so the difference is due to the
removal of soluble silver salts. The question, therefore, is whether any
insoluble salts are also present, which would need to be fixed out - if
toning still had an effect after 10 minutes' washing, whatever got toned
can't have been very soluble, so I'd say the answer is "Yes" (and that
further washing would not reduce the toned density any further!). Insoluble
salt does form in VDB and can be seen as a precipitate in old solutions, but
are tiny, insoluble particles also suspended in the liquid?
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.
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.
Liam
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.
Liam
-----Original Message-----
From: rurmonas@senet.com.au [mailto:rurmonas@senet.com.au]
Sent: 05 December 2002 09:45
To: alt-photo-process-l@usask.ca
Subject: VDB test results - part 1
Last night I ran some tests on the the need for fixing with
VDB. For the impatient, just read the conclusion below.
I used 3 types of paper (Rising Stonehenge, Canson Cartridge,
Canson Colorline). The reason for choosing three was to get a
spread of clearing behaviour. Stonehenge clears easily, the cartridge
clears more slowly, and the Colorline shows a slight stain even after
extended washing. I took two pieces of each and coated about
2/3 of the surface of each. The uncoated section was to help
judge any staining later in the test. These were dried with cool
fan blown air.
One set of three papers was washed for a total of ten minutes.
First for two minutes with continuous aggitation, then in
two changes of water for 4 minutes each with intermittent
aggitation. All water used for the above was tap water with
a pinch of citric acid added to ensure it was close to neutral
pH. The second set of three papers were washed for 2 minutes
with continuous aggitation. This was in water which had been
filtered through both mechanical and carbon filters.
After the washing I examined the paper (while still wet).
As expected both Stonehenge had no visible stain. The cartridge
after 10 min wash was clean, but after 2 min wash showed a very slight
amount of stain. The Colorline showed slight stain in both samples.
I then placed the paper into Agfa New Viradon (polysulphide) toner.
All papers darkened very quickly. I continued to tone for 10 minutes,
then washed and air dried the paper.
All papers showed significant brown colouration on the coated part.
This was about the same as "mid tone" on a VBD. Interestingly
the colour is close to that of a normal VBD, unlike the yellow-brown
that resulted from trying to tone a fully processed VDB print.
The papers which had been washed for 10 minutes were slightly
less dark than those washed for 2 minutes. This suggests the
silver content could be removed by washing alone, but I suspect
it would take hours to acheive this. The degree of staining was
different between the three papers, but in all cases was significant.
CONCLUSION
VDB prints contain signifiacnt amounts of silver in unexposed regions
after washing. This is true regardless if any visual staining is
present or not. VBD prints need to be fixed. I suspect the minimum
fixing time will probably vary with paper etc.
Richard
--- Richard Urmonas rurmonas@senet.com.au ------------------------------------------------- This mail sent through SE Net Webmail http://webmail.senet.com.au
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