The Plastic Deformation of Optical Glass

JSGT 1950 V34 T069-T076

A comparison was made of the impressions produced under given loads by a pyramidal ended diamond indenter in fluorite, in calcite samples with surfaces both normal to and parallel to the optic axis, and in fifteen types of optical glass. The most perfect rectangular impressions were obtained in fluorite, in the glasses a "pin cushion" being the usual shape. Diamond pyramid hardness numbers were calculated. The highest values were recorded in the case of barium crown glasses and the lowest in the flints, the hardness falling off with increase of lead oxide content. The displaced material resulting from indentation was piled up round the sides of the impression in a mound. Some observations were made on the furrows produced by drawing the loaded diamond point across the glass surface.

E. Wilfred Taylor