Strength of Thin Chemtempered Lenses

Static load tests were conducted on heat‐tempered and chemtempered piano white crown glass lenses from five different optical laboratories. With both ball‐on‐ring and ring‐on‐ring loading, chemtempered lenses considerably thinner than 2.0 mm were found to be as failure resistant as 2.0‐mm‐thick heat‐tempered lenses. A similar result was obtaind previously using the drop‐ball test. It is shown that the theory of brittle fracture can be used to relate the results of different tests and provides a rational basis for comparing the relative performance of chemtempered and heat‐tempered lenses.