We previously discussed this topic. https://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.