>Pyrogallic acid, 100g
Pyro = Pyrogallic acid or Pyrogallol (plus some other names). Not the same
as gallic acid. Gallic acid is manufactured from oak galls (among other
natural stuff) while Pyrogallic acid is made from (at least originally) coal
tar products.
Interesting in the history of photography that the action of an extract of
oak galls was found early to aid in increasing the sensitivity of silver
materials; it was used in some of the earliest formulas. But Pyro is
cheaper, more uniform, and became the developer of choice during the
wet-plate period and for some time thereafter. It is a staining developer
(somewhat chromogenic) and deposits a yellow dye along with the silver to
give very fine images. Keep it off your hands, though, as it stains badly.
During the 1930's and 40's, there were a number of derivatives that were
non-staining, but they never became popular.
Sil Horwitz, FPSA
Technical Editor, PSA Journal
silh@iag.net