I was told by Victor England of CNG that blue patina comes from human graves finds. I was then told by Ardatirion that Victor is prone to embellishment when he's full of wine. I'm going with the grave find because it's cool.
The grave thing sounds like a good choice to me. BTW, can you show both sides to this coin. This side looks marvelous!
Naw, Blue Patina means buried with the coin in the persons MOUTH so that they could pay Charon to cross the River Styx... Charon accepted it, and it turned blue in his skeletal hand... C'mon let's get it right folks!
Great coin!! ... congrats SWK I have a cool bluish example (humble, but still pretty cool) Gordian III, Cappadocia, Caesarea-Eusebia AE21 238-244 AD Dated RY 4 (AD 240/1) Diameter: AE21 Weight: 8.24 g Obverse: AV K M ANT ΓOPΔIANOC, laureate head right Reverse: MHT PO KAI B N, calathus containing five grain ears Reference: Sydenham, Caesarea; SNG Hunterian; SNG von Aulock; SNG Righetti; Lindgren & Kovacs; Lindgren III; MPR II Other: VF, some cleaning marks … extremely rare … apparently an unrecorded type for Gordian III (oh, and it was found beside a dead body ... no really ... *hic*)
You can call it "blue patina" - I'll call it active corrosion. I believe the ancient collectors use "bronze disease." Nevertheless, it is a beautiful coin.
While I am not a chemist, I have enjoyed cleaning things including coins for 50+ years. In my opinion, whenever I see bright green or red encrustations on a copper/bronze coin, 99% of the time it is active corrosion. The key word here is BRIGHT (active). As I wrote, I believe most ancient collectors call anything green on a copper/bronze coin "patina." When the surface has "set" it is no longer active and the green patina protects the coin from further deterioration. Bronze disease can be brown, green, whatever. I think of it as acid rust . The OP's coin has active green RUST residue that is eating it away. Nevertheless, it will not dissolve away until long after we are gone so many more collectors will be able to enjoy its beauty. PS That "green" is also a little too "modern-looking" if you get my drift...
Bronze disease is a very specific chemical reaction and it doesn't appear to be present on any of the coins in this thread. Rust occurs with iron, not bronze. I have no idea what you mean by acid rust. I've never heard that terminology with ancient coins.
As I have learned "bronze disease" is an internal acid reaction going on inside the coin. In many cases the outside of the coin turns green when this reaction is present. I used the term "rust" to keep it simple. You are correct, no one uses "rust" when talking about coins - they say oxidation. Anyway, since you possibly know what's going on inside the OP's coin, call it whatever you wish - how about blue-green patina? I choose to believe the coin is CORRODED.
Bronze disease can penetrate deep into a coin and be active while exhibiting no signs on the surface. But it would not cause this color change on the surface.
