Flint glass is an optical glass that has a very high index of refraction and a low Abbe number. Flint glass contains lead which gives the optical glass some of its properties.
Glasses are considered to be solutions instead of chemical compounds. They are comprised of silicon dioxide, sodium oxide and calcium oxide. Each type of optical glass has a different composition by mass. Flint glasses contain all of the previous ingredients plus around 45 to 65 percent lead oxide. Due to its unique composition, flint glass has high density, high dispersion and high refractive indices. Other types of optical glasses include barium glasses and crown glasses.