Knowing the difference between glass and crystal glass can be extremely difficult these days. A wide variety of vases, dishes, bowls, stemware and decanters are available in glass or crystal and with emerging markets mass producing such items, it can be difficult for consumers to verify producers claims especially as lead crystal glassware can come in various percentages of lead from 18% to 40%. So how is it possible to tell the difference. One way to tell the difference between crystal and glass is that glassmakers can blow crystal thinner than glass due to the binding qualities of the lead oxide. Closely examine the cut of the object. Manufactured glass has seams; being more brittle, the cut will not have the same accuracy or finish.