Instructions
Look for a glossy shine on glass marketed as crystal; run your fingers over any decorations. The edges are typically crisp and sharp, because they are hand-cut. Smooth, undefined decoration -- and seams running down the sides -- are signs of inferior quality, press-molded glass.
Look at the base for signs of wear. A vintage piece of crystal usually has numerous tiny scratches from daily contact with hard surfaces.
Check the item for any original labels. Glass is unlikely to show many signs of age, but a paper label features deterioration and font choices indicative of a specific era. Original packaging is usually a reliable indicator of age.
Consider the item's purpose. Pieces of glass used in formal functions were more popular in the past than they are today. Punch bowls, salad dishes, sandwich plates and decanters are often vintage.