1) Glass composition 
Lead glass is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40 weight% lead(II) oxide (PbO), while modern lead crystal, historically also known as flint glass due to the original silica source, contains a minimum of 24% PbO. Lead glass is desirable owing to its decorativ...
glass, containing a high proportion of lead compounds to increase the attenuation of radiation passing through it, used as a transparent protective barrier
Glass containing lead oxide as a flux.Called flint glass.
Discovered by George Ravenscroft in 1673. Often (not strictly correctly) called Flint glass, it contains Lead Oxide, as opposed to Potash glass or Soda glass. It cools rapidly, making it hard to manipulate into complex shapes, but its hardness and brilliance make it well-suited to cutting and engraving
[n] - glass containing lead oxide
noun glass containing lead oxide; has a high refractive index