“Crystal” was a marketing term widely used in the 20th century to distinguish hand-blown or better-quality items of transparent domestic glassware from the cheap press-molded variety; it has no technical or legal meaning, and isn't applied to colored or art glass. It is sometimes confused with “rock crystal,” a transparent semi-precious stone used in jewelry. Bowls are vessels with a central well capable of holding liquids and solids without leakage. Distinguishing a crystal glassware bowl should be moderately easy if you follow these simple steps.
Inspect the shape first. Bowls can range in size from individual dessert dishes to medium-sized salad bowls to enormous vessels for serving punch, complete with matching cups.
Look at the glass. It should be colorless, with a glossy shine, and there should be no vertical seams running down the sides. Glass that is slightly grayish and lusterless and that does indeed bear those seams will have been cheaply press-molded – that is, squashed into shape via a rapid mechanical process – and hence doesn't warrant the term “crystal.”
Run your fingers over the decoration, which on most crystal bowls should consist of crisp hobnail or star cutting made by hand or machine. It should feel pleasantly sharp-edged to the touch, whereas the decoration on cheaper bowls will lack definition. Also take a look at the base, which on good-quality pieces will often be finished off with a star-cut pattern.
Tap the bowl with your fingernail. A dull thud would suggest that there is a crack in the glass.
If buying a crystal bowl secondhand, be very patient in checking for damage, as all kinds of chips and blemishes can lurk among the hobnail cuts.