A study seeking to decrease the brittleness of glasses was carried out. The brittleness, defined as the ratio of hardness to fracture toughness, was estimated from the ratio of median crack length to the diagonal length of a deformation impression. The brittleness of various kinds of glasses in the silicate as well as borosilicate systems was investigated as a function of glass properties. The brittleness of the glasses was correlated with densities, i.e. a variation of ~1-~9um-1/2 in brittleness was observed as the density varied from ~1.0-~2.8g/cm3. The brittleness of normal glasses decreased with decreasing density due to the ease of both plastic flow and densification. On the other hand, the brittleness of anomalous glasses increased with decreasing density due to the lack of plastic flow.
