We previously discussed this topic. http://www.forumancientcoins.com/board/index.php?topic=64867.0
In Classical Deception
(page 54) Wayne Sayles
mentions the excellent patinas on Sicilian fake coins
starting in the 1990s. After his
book was published I noticed copies of the coin Sayles used as an example appearing in the printed catalogs of several dealers.
Mezzasalma, Mondio, and Serafino analyze five fake
bronze coins with false patinas. This is the recipe the forger confessed to:
“…one of the most used recipes for fakes
artificial ageing utilizes a solution composed by penthydrated CuSO4 [Copper Sulfate] together with HNO3 [Nitric Acid] and NH4Cl [Ammonium Chloride] in distilled H2O [Water]. In this solution, warmed up until 80‐90°C, the just produced fakes
(at about 100 °C) are immersed. Such a bath gives them an artificial patina
with an “antique green” colour and a deceptive antiquity
appearance. Drops of the above CuSO4 solution on clean bronze surfaces may form dendritic structures with the same characteristics of those observed in our fakes
I wish I knew of an easy way to analyze real and false patinas and categorize them. Dealers just give colors. I wish there was something like the "lead test" kits they sell at home
depot to analyze patinas with a few easy swabs.