Fake 20 mark gold coin [решено]

Hello everyone!

I got this fake 20 mark - William I coin. I (now) know it's fake because it say 1894 and this coins, with this ruler's face on it, wasn't minted that year.

The jewelry store from were I've bought it, ensures me that it's made of gold .900. They say that they can prove it with a machine. I guess they are talking about a XRF analyzer. As far I know those machines only analize the surface, right?

There's any other non destructive method to test what it's made of?

Best regards,

Leo

See https://en.numista.com/numisdoc/determining-the-metal-of-a-coin-27.html

Can you take an image of the edge, and one with a mirror to see both sides at the same time? It will be interesting to see how someone has managed to get two sides of 2 different coins together as one coin, or if someone has struck a fake coin with wrong dies for the date (which is a pretty dumb mistake) as the eagle from William I is completely different! 
 

In answer to your question, weight of gold (the coin) to spicific dimensions will help you determine whether it is gold, but considering it is meant to be a gold coin with two sides from two different coins it is likely not going to be gold either. Unless the jewellery sold it to you as as something other than a real coin, (gold token, copy etc) they are guilty of selling you something under misrepresentation anyway - irrelevant if it is gold or not, you are fully entitled to a full refund. I would recommend you ask for that, and contact local authorities with your receipt anyway.

Depth of penetration of XFR equipment ranges from 0.001 mm to 2.0 mm depending of the exact equipment and parameters used. In other words, assume it only gives surface composition unless proven otherwise. 

Luckily, today I replaced the coin for a 1888 variation.

They tested it with a Thermo Niton XL2 and the result was .900 gold, but I told them that equipement only test the surface composition and they offered me to replace it without any problem.