Crystal is much more brilliant, sonorous and resistant than even the best glass as its components are nobler.
Bohemian crystal for example contains over 24% PbO as prescribed by the law (the lead content gives the glass a crystalline sparkle).
What's the difference between crystal and just plain glass?
Purity, as well as the addition of various metals, most often lead, is an identifier of crystal. But lead is only needed for crystal that will be decorated by cutting. Other metals are used for creating textures and qualities for each technique.
Different substances are used to color the glass. For example, the rich ruby tone includes pure gold, which makes all red colored products slightly more expensive.
High quality crystal usually has a "ring" when struck by a fingernail and is absolutely clear, hence the phrase crystal clear. Fine crystal hardens and is able to withstand more impact than regular glass, although it is more likely to chip. A crystal goblet is much less likely to shatter when it falls on the floor.
There is, in fact, a difference between glass and crystal, but it varies from country to country. To most of the Western world, "crystal" signifies the presence of lead. Under European Community regulations, glassware containing less than 4% lead oxide is defined as "glass", that with a lead content greater than 10% is "crystal" and if the content is 30% or above, the designation is "high lead crystal". In the United States, glass must contain at least 1% lead to qualify as crystal.
To the Czechs, however, it is more a question of semantic. The term "crystal" can be applied to any refined, high-quality glass. Lead crystal is understood as having at least 24% lead. Lead content tends to soften glass making it more amenable to cutting and engraving. Lead also adds weight to glass and makes it refract light, so that rays shining through it will splinter into the colors of the rainbow.