Q: What is the difference between crystal and glass?

A: The answer is "c." Crystal has a lead content of at least 24 percent whereas glass has no lead.

Generic terms: The tumblers stored in most people's kitchen cupboards are referred to as the "everyday" glassware. These items have a sturdy, almost indestructible quality that helps them withstand hundreds of dishwashings and plummetings from counters and tables. The glassware reserved for finer use-goblets with etched designs and pencil-thin stems, for example-often is called crystal. But is it really crystal?

Crystal often is used as a generic term for any glassware that has a form more elegant than the glassware or jelly jars used every day. Nevertheless, it is not always an accurate label.

Maintaining standards: According to John Kennedy, head of technical services at Waterford in Waterford, Ireland, there are very specific guidelines for what constitutes real crystal. Kennedy notes the three primary criteria for crystal: a lead content in excess of 24 percent, a density in excess of 2.90 and a reflective index of 1.545. These specifications were established in 1969 by the European Union, the main trading block of 15 European countries. The United States, Kennedy says, never established its own criteria, but accepts the European standard for customs purposes.

Getting the lead out: According to Kennedy, the key ingredient in crystal is lead. Waterford crystal traditionally has a lead content of about 32 percent. Although some finer glassware may contain lead, anything below the 24 percent standard is not considered crystal. Common glassware contains about 50 percent silica (sand), but no lead.

Is it real? Distinguishing real crystal from crystal wannabes can be difficult. According to Kennedy, only an expert can detect real crystal by sight. Nevertheless, there are a few distinguishing characteristics that help in detecting the real thing. Because of the high lead content, crystal rings when tapped ever so gently and is heavier than common glassware. It also has a bright, silvery color. When held in the right position, the refraction and dispersion of light from crystal creates a rainbow of hues.