Quick Composition Question

My suggestion is to take a dime from 1966 or earlier and stand it on end and twirl it like a top. As it spins and lands flat, note the sound it makes. Then twirl the unknown dimes, the sound of the 80% silver should make the same sound as the dimes from 1966 and earlier. That should help with the 80% silver. To double check the 50% silver, do the same thing with the 1968 50% silver dime, if you know that the 1968 dime you are using is the 50% silver dime. This is not a perfect method, but may help, I have used this method before.

With a little practice, you can tell them apart using the ring test. Just drop it several inches off a hard surface and note the ring it makes. As uncle al mentioned, use a '66 or earlier and a '68 to practice telling the different tones apart.

As already noted, it is not exact science...

I use the same method to tell sterling from .500 U.K. coins.

Other than getting them assayed, or using a Niton analyzer, http://www.niton.com/Metal-and-Allo...px?sflang=en , I don't know of any other way to tell them apart.

I would think a specific gravity test would tell you the difference. Any jeweler should be able to do it.