Information from the Getty AAT
crystal (lead glass)
Fine, high quality, heavy, decorative glass made with fine white sand, at least 24% lead oxide, and small amounts of potash and niter. It is clear, colorless, highly refractive glass that is heavy and has greater than twice the density of standard borate glass. It was developed in England in 1676; often used for high quality chandelier prisms and fine stemware.