We often see posts asking if we think a coin may be genuine.
Usually only a picture with little or no details.
Some replies mention the need to know "Density" or "Specific Gravity".
At least two very short easy-to-do methods can be found online by searching terms like Home Density Test or Using Water to Prove Gold. Density and Specific Gravity would be another good search term.
The examples are very similar to what I do in the case of large coins like Chinese Dollars as well as many other types of coins that should be silver.
I've since found more and came back to edit saying there are many more than just the ones I began with- including another: How to Test Silver and Gold at Home