Translation of legend abbreviations:

A(VTOKPATΩP)   K(AICAP)  M(APKOC)   A(VPHΛIOC)   NOVEMPIANOC  CEB(ACTOC)

Imperator Caesar Marcus Aurelius Numerianus Augustus

L Γ

year 3

EGYPT, Alexandria. Numerian

year 3, CE 284/5

potin tetradrachm, 20 mm, 7.25 gm

Obv:  AKMANOVMEPIANOCCEB; laureate draped bust right

Rev:  Nike flying right, holding wreath; ETOVC - Γ

Ref: Emmett 4022(3), R2; BMC 2469

CNG e324, 9 April 2014, lot 707

This coin came from a large lot of Alexandrian tetradrachms, most of which had been "treated" by a previous owner with what appeared to be women's makeup, mimcking a sandy patina.  Fortunately the makeup was easily removed and hopefully no harm done.  I soaked the makeup off all the coins, treated with Verdicare, and I inspect them regularly.  The makeup does appear to have caused corrosion (verdigris) underneath but hopefully the rapid corrosion has been halted.  

 

This is the problem I have with applied patinas-- what might they be doing to the fabric, out of sight?   I routinely soak my newly acquired bronze coins in water, acetone, and alcohol (some or all, separately) and treat with Verdicare if there is any suspicion about the patina.