How We Authenticate Coins — Patina
Our authentic coins have traveled though hundreds of years. Usually, buried in clay jars -- or else in shipwrecks. They have not had easy lives!
As part of this exposure to the elements, chemical reactions happen on and near the surface of the coin. This causes discoloration, and the formation of a crust. The exact pattern tells a secret history unique to each coin. We lightly clean our coins, to keep this layer largely intact -- after all, it would be a shame to go through all the trouble of sourcing beautiful authentic old coins just to make them look like new!
Anyway, this layer has some useful properties when identifying real coins:
In the image featured in this article, the top row of coins are genuine and the bottom ones are not. In the upper left, you can see the patina on a completely unprocessed coin. We gently abrade away some of the clay and oxidation so the features are more visible. The top middle coin is a genuine coin that was stored in clean and dry conditions for hundreds of years -- while you don't see a 'crust' on it, the top layer is still a little shiny and glassy. The top right coin is a genuine Chinese coin in good condition, about 1000 years old. This is an example of a genuine coin with black patina -- to contrast with the coins that have fake black patina in the bottom row. Also note the particles of clay cemented to this coin (these are very difficult to remove).
For the fakes (bottom row), notice the patina is very slight and looks burnt, or perhaps painted on. This patina does not 'catch the light' like a real one, so it lacks the glassy appearance when polished. Also notice that they have exposed metal. Bronze/brass is a moderately reactive metal, and examples without corrosion are uncommon (and in any case would look more like the top middle and top right examples).
As part of this exposure to the elements, chemical reactions happen on and near the surface of the coin. This causes discoloration, and the formation of a crust. The exact pattern tells a secret history unique to each coin. We lightly clean our coins, to keep this layer largely intact -- after all, it would be a shame to go through all the trouble of sourcing beautiful authentic old coins just to make them look like new!
Anyway, this layer has some useful properties when identifying real coins:
- It must have texture.
- It must have color variation -- almost never just black.
- It must have some thickness to it, going a little bit deeper than just the surface.
- It's surprisingly hard ! You can polish it to a glassy sheen, which looks nice on some coins (we do this sometimes for our product -- it depends on the coin).
- Has no texture.
- It is almost always just black.
- Is a very thin layer.
- Is usually not very hard.
In the image featured in this article, the top row of coins are genuine and the bottom ones are not. In the upper left, you can see the patina on a completely unprocessed coin. We gently abrade away some of the clay and oxidation so the features are more visible. The top middle coin is a genuine coin that was stored in clean and dry conditions for hundreds of years -- while you don't see a 'crust' on it, the top layer is still a little shiny and glassy. The top right coin is a genuine Chinese coin in good condition, about 1000 years old. This is an example of a genuine coin with black patina -- to contrast with the coins that have fake black patina in the bottom row. Also note the particles of clay cemented to this coin (these are very difficult to remove).
For the fakes (bottom row), notice the patina is very slight and looks burnt, or perhaps painted on. This patina does not 'catch the light' like a real one, so it lacks the glassy appearance when polished. Also notice that they have exposed metal. Bronze/brass is a moderately reactive metal, and examples without corrosion are uncommon (and in any case would look more like the top middle and top right examples).
