Optical glass: They contain phosphorous as replacement for most of all the silica and lead silicate, containing a little CaO₂, the latter is capable of absorbing ultraviolet light which is injuries to eyes. Moreover, they are given through homogeneity. This is achieved by a very careful manufacturing process and by careful heating of molten mass of prolonged time. In, general, optical glasses have low melting points and are relatively soft. Their chemical resistance and durability are appreciably lower than those of ordinary glass. They are used for making lenses.