1775 Mexico 8 Escudos - Tests 91%+ Au, But Low Weight - Counterfeit ?

This interesting. I don't know how it was made, maybe drilling into the coin through the edge and replacing the gold? There are no known underweight "one offs" made at the mint. There are really good colonial gold counterfeits like I saw on display at a coin show. If this is a counterfeit made when this coin circulated ( contemporary counterfeit) it has value greater than the gold content.

Hi MasterKromm - I've read a little bit on the Sigma Metalytics analyzer and it is basically a metal detector. As a metal detectorist I can tell you from experience that it probably works best for obvious fakes with base metal cores. I would recommend a specific gravity test by water displacement to get better info, or an XRF test. That might be able to better tell you what kind of a contemporary counterfeit it is.

To try to answer you other question, it may be best to send it back for a refund if you are able. For 8 escudos, my observations have been that contemporary counterfeits sell well if they have high gold content or are gilt platinum. Also cruder counterfeits (e.g. struck with hand-engraved dies) do well. This is a nice piece but it doesn't seem to me like a slam dunk that it would sell for more than a genuine coin. Just my 2 cents and I look forward to hearing from other posters with more experience.