re: How to tell crystal from glass

Probably get more responses if you change the title to "How can you tell if it's Crystal or Glass?"

As far as your question goes, flick it. If it has a low pitched, thud sounding ping, it's glass. If it has a higher pitched, more musical sounding ping, it's crystal. Crystal is usually thinner than glass and is always clearer than than glass, which is more cloudy than crystal. Crystal also produces a prism when held to light where as glass does not. Crystal is heavier than glass. If you wet your finger and run it across the rim of the cup, crystal sings ( ) in a higher pitch. While glass does sing when doing the same, the pitch is distinctively different (similar to the sound when flicking it).