So... Is Patina Good Or Bad?

It would depend on if the patina is attractive or not.

A real nice patina will raise the value....a real nasty one can decrease the value.

Yes, and a bad one can make a relatively nice coin almost worthless.



I try to avoid this red stuff. It seems nearly impossible to remove.

One reason patina is good is because of what it is. The ground the coin is buried in reacts with the metal in the coin, so the patina is actually partially the original metal in the coin that has gone and formed an oxide. This means that if you remove the patina you are actually removing part of the original coin, and likely removing detail that is only visible with the patina. It is important here to differentiate between patina and encrustations. Encrustations are usually dirt that has hardened around the coin, and sometimes completely obscure the coin until they are taken off. Learning to remove encrustation and leave patina is a pretty decent, though incomplete, definition of what cleaning ancient coins is.

Also the above only applied to bronze coins. Silver coins don't really develop a patina* due to the much lower reactivity of silver compared to bronze, so removing what does develop on them isn't likely to damage the coins details like doing the same to a bronze coin would. It may damage the aesthetics of the coin, though.

*Before anyone yells at me yes some silver oxide forms, but the word "patina" generally refers to a protective layer, while what forms on silver is typically not nearly thick enough to protect anything.

Good patina does raise the value of a coin, and often a patina can be modified (olive oil very slowly darkens patina, so you could put something in there for a couple of years and hope for a nice even black tone at the end). However, if you remove it, you destroy a coins value.

Take this coin I owned, that I bring out at every opportunity. If the finder hadnt taken off the patina, we'd be looking at 5 figures, probably between 10 and 30 thousand pounds (its a unique Carausius, new bust type in very good artistic style, which the experts think shows Carausius riding a chariot).

How did you arrive at that figure?

Might be a bit optimistic Ben, but a nice example all the same. I do have some coins of Carausius that I have hung onto just because I could not find them listed. They are pretty similar to the last one you purchased but with a very different portrait.