Richard Knoppow (dickburk@ix.netcom.com)
Tue, 25 May 1999 13:27:37 -0700
At 08:12 PM 5/25/99 +0100, you wrote:
>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.
>
This is in fact Nelson's formula complete to some of the wording in the
patent.
>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
>
>
>
>
Nelson's is the only toner which seems to require this. Gold toners for
blue or for modifying sepia to red do not recommend re-fixing.
My first thought is that the relatively hight temperature required by
Nelson's might make hardening after toning desirable and a bath in
hardening fixer would accomplish that but I don't see any such
recommendation for other high-temperature toners.
My suspicion is that either Nelson's re-halogenates some of the silver or
Nelson thought it did. That would certainly require fixing.
Fixing would have no effect on metallic silver deposited on the emulsion.
The McGraw-Hill chemical dictionary defines Ligand as: The molecule, ion,
or group bound to the central atom in a chelate or a coordination compound.
I don't know what significance this might have here. Perhaps Sil or
someone else with good chemistry knowledge can explain all this.
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com
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