Some Properties of Polished Glass Surfaces

The optical glasses made by combining silica with various other oxides are similar in that the silica will not dissolve in water or weak acids at the same rate as the other materials contained in the glass. This property of silicate glasses is involved in the accidental formation of colored stains on the surface of dense lead or barium glasses exposed to the weather, in the formation of surface haze on lenses exposed to tropical humidity, and in the formation of silica low-reflection films on glass by chemical treatment. — Quantitative data have been collected on the tendency to form surface stains and on the rate of dimming for all the common types of optical glass. Surface stains do not harm a lens and may increase its efficiency. Any haze that forms on a lens exposed to a humid climate should be removed by careful cleaning. — Purposely formed silica surface films for increasing the transparency of glass are identical with the stains that form accidentally on dense lead and barium glasses except that they are of controlled thickness and may be stabilized to prevent any further increase in thickness. Chemical methods are now available for forming low-reflectivity surfaces on all of the common optical glasses. Proper heat treatment of these silica films will lower the rate of solution of the glass. The durability of a lens is greatly improved by this process. — The gain in light transmission that results when a silica surface film is formed by chemical treatment is less than that produced by films of low-refractive-index fluorides evaporated by the Cartwright and Turner method. There is no doubt but that both the evaporation process and the chemical process will be used in the optical industry. Each process has advantages depending on the circumstances of use.

Print ISSN

0097-5834

Published

1941-09

Content type

Original Research

DOI

10.5594/J09968