RE: Judy's Ferric Ammonium Citrate Puzzle
Philip Jackson (pjackson@nla.gov.au)
Mon, 09 Dec 96 20:16:00 PST
A slightly earlier date indicating availability of green ferric ammonium
citrate is a 1897 article by Valenta on "The Use of Various Iron Salts in
Printing Processes" from the Photo. Corresp., an abstract of which I came
across in the Photographic News, 5 Mar. 1897, p. 152. It almost certainly
would have been reprinted elsewhere - as Judy mentioned the photographic
journals of this era apparently ignored copyright, although the first Berne
Convention was effective from 1887. Maybe fair use was fairer then, the
diffusion of knowledge triumphed over the greedy curtailment of capitalistic
monopolies, or more likely the journals had reciprocal agreements, as long
as the source was acknowledged.
Anyway, Valenta describes experiments with commercially produced green
varieties then available in Germany, notably one from Merk [sic] of
Darmstadt; he also quotes an authority called Rother who gives three
different formulas - one for a neutral and two for acid salts. There are
also single and double salts. According to Valenta, dilution of both the
ferric ammonium citrate and potassium ferricyanide should vary slightly
according to the constitution of the chemicals.