Antique crystal -- at least 100 years old or older -- contains lead, which makes it much heavier than glass. The lead oxide added to antique crystal made it easier for glassblowers to shape the crystal without the constant need to reheat the glass. It also made the glass more pliable to use with molds. The manufacturing process for leaded crystal makes antique crystal stemware twinkle and sparkle when the light hits it just right.
When crystal stemware is held up to sunlight, it acts like a prism and splits the rays of the sun into rainbow colors. To determine if your stemware is crystal, lightly and gently tap the bowl of a wine glass with a spoon. If it produces a nice ring, almost like a bell or small chime, it's real crystal. If it doesn't, it's just glass, not crystal. You can also lightly wet the tip of your finger and run it around the lip of the bowl to make the crystal sing. If it doesn't produce a musical note, it's not crystal.
Artist's or Maker’s Marks
Crystal makers often added an identification mark to the bottom of stemware by acid-etching a logo, trademark, symbol, artist's signature, letters and numbers. some manufacturers didn't etch the glass, but if you get lucky, you may find an old paper label still stuck to the bottom containing the manufacturer's trademark or logo. Turn the glass over and examine the foot carefully in good light with a magnifying glass. If you find a mark, compare it to manufacturer's marks by visiting online replacement sites, or compare the marks to those found in one of many books on antique crystal and pattern identification. For instance, Baccarat crystal in France, which made crystal for royalty beginning in 1823, usually etched the company's name onto the bottom of the stemware base.
Crystal makers etched or cut clear and colored crystal in specific patterns and designs. Cut crystal has rounded edges, as opposed to cut glass with sharper edges. Once you know the manufacturer, you can identify the pattern by comparing it to others at online replacement sites, collector or even manufacturer's websites, which might help you determine when it was made. Crystal that is less than 100 years old is not considered antique.
Replacement companies carry a variety of crystal stemware glasses in case you need a replacement water goblet or wineglass from the family crystal set. Some of these companies also provide assistance in helping you identify antique crystal. When you work with online replacement sites, contact them by email or standard mail, and include a clear picture of your stemware. Photograph any visible marks to help in the identification.