The addition of up to 30% lead oxide, ( though most manufacturers are reducing it to 24%, the legal minimum to be called lead crystal ), gives crystal glass a high index of refraction which makes it sparkle when cut at sharp angles, is softer to cut, and gives the glass a distinctive long lasting ringing tone when it is struck gently with a hard object like a fingernail. The lead may under very extreme conditions leach out into acidic beverages, like white **** or Orange Juice ( if stored over night in a fridge for instance). The glass is also more fragile and subject to temperature shock: Crystal glass will often break when cold water is poured into a hot glass or vice versa. Glass is a liquid in the sense that it does indeed flow, but it flows over an extensive period of time. The difference between a crystal and glass, is that a crystal has a homogenous solid formed by a repeating,