on a glass...wet your finger and run it around the rim...if it "sings" it's crystal...if not it's plain glass

The meaning of crystal versus glass changes according to the country. The word "crystal" means, in most of the western world, the presence of lead. According to European Union rules, glass goods containing less than 4% lead are defined as "glass". Goods containing more than 10% lead are defined as "crystal", and goods containing more than 30% lead are defined as "highly leaded crystal". In the USA it is the opposite - glass is defined as "crystal" if it contains only 1% lead. In the Czech republic, the term "crystal" is used for any exquisite, high quality glass. Leaded crystal means crystal containing more than 24% lead oxide. The presence of lead in crystal softens the glass and makes it more accessible for cutting and engraving. Lead increases the weight of the glass and causes the glass to diffract light. Glass can contain up to 40% lead, if maximum hardness is desired. On the other hand, crystal can contain less than 24% lead if it has a high proportion of barium oxide, which ensures high quality light diffraction. The difference between glass and crystal is evident to the eye, and we can see it when a crystal chandelier casts color spectrums through the whole room. The higher the lead content, the more dazzling the chandelier. http://www.luckyglass.cz/en/crystal_glass.html

well, you cant smoke glass...

If you are talking crystal vases that you collect for your curio cabinet, just thwack it with your finger if it rings it is crystal If it just goes thwack it is only glass.