Liam Lawless (lawless@vignette.freeserve.co.uk)
Tue, 25 May 1999 20:12:57 +0100
Hi Folks,
Few texts seem to mention the need for fixing, but, in Clerc:
"The fact that the toning bath always contains silver salts led Blakeland to
advise subjecting prints toned in it to re-fixation in a new bath. It is to
be regretted that this precaution is usually neglected, with the result that
a slow yellowing of the whites of the print may ensue."
Somewhere in this thread it was suggested that fixing should not be
necessary because of the hypo in the toner but I think this is incorrect
because fixing is a two-part process whereby silver salts are first changed
into an insoluble silver-thiosulphate complex, and then, in the presence of
sufficient free hypo, to a soluble silver-thiosulphate. The second stage
does not occur if the bath is saturated with silver, even if it still
contains free hypo, and the insoluble silver-thiosulphate left in the print
as a result eventually breaks down to form silver sulphide. A hypo-alum
toner, which is reusable almost indefinitely, will become saturated with
silver at some stage, and prints toned in it are likely to stain in time.
The literature is littered with hypo-alum-gold formulae, and the best place
to look is probably in books from the 1930s, or thereabouts. Following a
big clear-out a few months ago, I don't have many books on the shelf, but an
example from "Henley's Twentieth Century Book of Formulas, Processes and
Trade Secrets" (a great little book!):
Water at 125 deg. F 1 gall.
Hypo 2 lb.
Dissolve the hypo completely, then add 4 oz. amm. persulphate. If the bath
does not turn milky, heat again until it does. Then mix in the following
solution, precipitate and all:
Silver nitrate 80 gr.
Table salt 80 gr.
Water 6 oz.
(Note:1 grain = 0.0648 grams; 80 gr. = 5 grams, near as dammit)
When completely dissolved, after allowing the combined baths to stand a
short time, mix the following stock solution and add 4 oz. of it to the
above:
Water 8 oz.
Gold chloride 15 gr.
Use in the same way as ordinary hypo-alum, and "liven up" when necessary
(after 40-50 8X10s) by adding 4-6mls of the gold solution.
Said to give richer browns than ordinary hypo-alum. Charles Walley, in a
book I no longer have, said that hypo-alum-gold gives sepias that are
"unsurpassed by any other process". I tried the Walley recipe, and didn't
find that the gold made a significant difference. But he'd have been
writing about 50 years ago, when, I suspect, papers were rather different.
I was once told by a chemist that prints toned with gold should be given a
short fix after toning. I never understood the reason, but it's something
to do with ligands (whatever they may be) which, if they are not destroyed
by fixing, have a harmful effect on the paper base in the long term.
Whether or not this also applies to hypo-alum-gold toning, I don't know, but
it's probably wise to assume that it does.
Liam
This archive was generated by hypermail 2.0b3 on Thu Oct 28 1999 - 21:39:35