What is most likely being discussed in the above captioned thread is
(C6 H8 O7) Citric Acid - a weak organic acid and often used as a
preservative in home canning.
Various chemical supply houses; or buy the (dry) lb (approx 11/2
kilo) from Daniel Smith Art Supplies (catalog # 284-130-006) $10.99
/ lb. That is not the lowest cost supplier; but, I can get most of
my etching supplies ordered/delivered all under the same PO and
shipment.
Remember ? C6 H8 O7 mixed with (Ferric Chloride) FeCl Edinburgh Etch
mordant - that is not intended as a formula. Refer to archives for
the Edinburgh Etch mordant discussion threads.
Regards,
Mark