I found this tester for coins. Bullion Test apparently you tap the coin near the microphone of your phone/tablet it analyzes the frequency that the coin is resonating and determines if its silver , gold, or fake Did anyone ever use it or heard of it? IS the silver content of a Roman Republic Denarius similar to a modern silver of- for example a mercury dime or Morgan Dollar??
You can find many threads here and other forums about people using the "ring test" on ancient silver coins. You don't want to do this. If the coin is heavily crystalline internally you might just break it. Roman silver coin purity fluctuates far more than that of modern coins and most fakes are made of the correct metal(i.e. most silver denarii are made of actual silver). I doubt that such a test could really provide reliable authentication information.
It could work to an extent. Many commercial testers works on comparison of ampitude/frequency with a chart or a recording of previous tests, but they use a carefully standardized generated tone and test the response with internal charts. When you generated a tone by tapping the coin, the sound produced will be dependent on the material tapped ( should be hard) and the coin, which should be in free fall. I do not like to drop my coins on a hard surface with a force to generate sound well. With bullion, fine, but with collectors or ancient coins, no. If you are going to drop bullion coins, just use jeweler's acids, more accurate. Its a cheap app and the developer seems to support it, so you could play with it. If you have a frequency generator and oscilloscope, you can rig audio equipment to do such. But I have to say, I have not had the urge to do so
The silver content of AR ancient coins varies considerably, but you can find lab analyses done for many types. Theoretically you should be able to ring test the 90% -ish ones (matching pre-1964 US silver), but in practice it just doesn't work. Try it yourself with a Roman republican denarius (high 90%s silver) and a 90% silver US dime. The rings aren’t even close. Whether this is due to crystallization, differences in the base metals in the alloy, annealing, the shape of coin, or something else I do not know. To test the surface, you can buy silver testing solution from amazon. It will stain the coin so test the edge. If you want a quick test for solid silver, you might try a silver slide. It works pretty well. Just be sure to put something over the magnets to keep them from scratching your coins.
Although it can't provide reliable authentication information it might be possible to calibrate it to give a hint how corroded the interior of the coin is. It would be hard to calibrate a digital "ring test" app.
