Expert: Dmitry Livshits - 6/29/2010

Question
I recently found a 1888 20 mark coin from Prussia (which I have been told are gold coins), however, my coin does not appear to be made from gold.  I was hoping you could help me figure out if it is counterfeit or something else.

Answer
Hi Kali,
There are many counterfeits and also novelty replicas (including antique and vintage ones) of old German gold coins. The quickest way to tell is by weighing it on a digital scale. A genuine coin in excellent condition will be between 7.9 and 8.0 grams. One with a lot of wear can be as low as 7.5 grams. Anything below 7.5 on a worn coin or 7.9 on a mint condition coin is a red flag for being a replica. If you do not have access to an accurate scale, I can also determine exactly what you have from a clear picture of the portrait side. Just ask a follow-up to this question and attach a picture to it.
You can usually tell a modern replica from an old one by looking at the details and materials used. Modern versions will usually be crude and made of a base metal with gold paint or that flaky leafing gold color that is found on costume jewelry. Older versions will sometimes be made of plain brass, but mostly copper or bronze with gold gilding on the surface. On these pieces the gilding often wears off, starting with the high points, showing the reddish material beneath the gold colored surface.
Also worth noting: acid testing is not always accurate for genuine antique gold coins. Unless you clean them with chemical solution dirt and minute oxidation on the surface of old coins will interfere with the acid test, unless you allow the edge of the coin to be cut or filed (thus damaging the collectible value). Many people believe that gold does not oxidize at all, but it actually does oxidize slightly over the decades.
Thanks for the question! =)