From: Liam Lawless (lawless@ic24.net)
Date: 04/28/00-07:40:36 PM Z
Hi Richard,
I've been experimenting with home-made POP emulsion for a few weeks, for a
little write-up for Judy. I've tried a self-toning version, without much
success so far, but have found out a bit about it.
Glafkides says that POP emulsion can be made self-toning with 2.5 g of gold
chloride (AuCl3 he says, though I think he means HAuCl4) or thiocyanate per
100 g of silver nitrate, added to the gelatin-salt solution before
precipitation. I've tried various proportions around that figure, none of
which seemed to make a significant difference, but more than 2.5 g per 100 g
AgNO3 causes some of the gelatin to coagulate in stringy lumps.
An old Ilford Manual of Photography (undated, but probably '30s-'40s) has
quite a bit of info about using POP & self-toning papers. The important
thing, apparently, is that self-toning papers are fixed straight after
printing-out, without an intermediate wash which, presumably, would wash out
the gold. Toning is supposed to happen in the fixer. I tried this & did
not get the staining I half expected, but neither did I get any toning. The
book says that the colour can be varied with the strength or temperature of
the fixing bath, becoming cooler as the toning action is stronger. (With
stronger/hotter fix the density loss is greater.) It does not say, though I
think it probably should, that a wash and fresh fix should follow.
With self-toning collodion POP, a salt bath before the fixer could also be
used to vary the tone, but this has little effect with gelatin POP.
Maybe my experiments didn't work because I didn't use enough gold. I used
what Glafkides said, but maybe he was referring to free silver nitrate, in
which case more gold would be needed. (But the problem with the gelatin??)
Will try again soon, but what I don't understand is how hypo reduces gold
salts, and only in the image areas at that. Gold chloride and hypo together
form what they used to call gold-hyposulphite, more commonly known as sel
d'or, but if this plays a part in the toning action, I'd expect it to
produce general fog. I've dropped a line to Mike Ware, but haven't had a
reply yet. Any ideas?? And have you got some self-toning POP?
If you still need the info, I can OCR it from the Ilford Manual. Let me
know.
Liam
This archive was generated by hypermail 2b29 : 06/13/00-03:09:50 PM Z CST