If you've been following this thread Mike Ware's paper is well worth looking
at even if you're as chemically illiterate as me. It's in the Journal of
Photographic Science, vol. 42 (1994): 157-161. Regarding different gold
complexes, he says that Herschel solved some of his initial problems by
avoiding the most commonly available gold complex, tetrachloroaurate(III)
and using the gold(III) salt, sodium tetrachloraurate(III). Maybe salt
contamination might explain Terry's accidental "lost chord"? Testing this
would, however, most likely be uncertain and very expensive.
Regarding the different gold complexes obviously there are significant
differences if the prices Terry quoted are any guide:
>> Which gold chloride ? My Johnson Mathey Catalogue lists gold chloride,
AuCl
>3 at
>> L795.90 for 5 g (glycine is on the opposite page for L 15.90 for 500 g,
this
>> comment is for those interested in 19 century developers). But H Au Cl 4
at
>> L110.50 for 5 g.
Luckily it looks like John has been able to use the cheaper option:
>3)I used the HAuCL4. I beleive this is known as
>hydrochloroauric acid, though my bottle of reagent is labled
>"gold chloride"
Presumably the AuCl3 could also be used (in different quantities) since what
you are actually producing is a soluble gold(I) complex in combination with
the ligand.
Now for a really grubby question. Mike writes, "Colloidal gold has very high
covering power, which mitigates the expense of using it for enduring
photographs." Roughly how much does it cost to produce a single print? How
does it compare to platinotype or Cibachrome?
Philip Jackson
pjackson@nla.gov.au