flint glass

Flint glass is any highly-refractive lead-containing glass used to make lenses and prisms. Because it absorbs most ultraviolet light but comparatively little visible light, it is also used for telescope lenses. Flint glass typically has a much higher refractive index than does crown glass, and exhibits much higher dispersion, however it is less resistant to damage. Flint glass is used in conjunction with crown glass to make achromatic lenses.