Inventors:
Ronald J. Tillen - Thompson CT
Donald E. Everburg - Southbridge MA
Assignee:
American Optical Corporation - Southbridge MA
International Classification:
G01N 100
Abstract:
The strengthening of a glass ophthalmic lens by ion exchange treatment does not alter the appearance of the lens sufficiently to render the presence or absence of such strengthening readily visually ascertainable even with the aid of a light polarizing strain detector. It being desirable to inspect for the presence or absence of strengthening by ion exchange treatment prior to dispensing glass lenses to the public, the present invention provides an auxiliary device for a light polarizing strain detector with which a lens to be inspected may be immersed in a liquid having approximately the same refractive index as the lens so that the strain detector can produce readily perceivable stress patterns in strengthened lenses.