Development of Hard Glasses*

A bstract This paper covers a phase of the work which was carried out for the Office of Production Research and Development of the War Production Board on the development of glasses of increased hardness for use as instrument bearings. A literature survey was made and a study started on the development of hard glasses for use in the manufacture of glass bearings. The data are of interest since information on the effects of a number of these oxides on the hardness of glass either have not been published previously or, in former studies, the amounts of oxides were not so large as those used in this work. Practically all of the work reported here was done either in the alumina‐silica‐boric oxide‐calcium oxide system or on glasses derived from this system by substitution of various oxides, chiefly for silica. The Knoop hardness numbers of the glasses are reported. Data were not obtained on the working properties of the glasses described herein. In addition to the footnote references, a comprehensive bibliography is given at the end of the paper.