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THE MANUFACTURE OF FUSED BIFOCAL SPECTACLE LENSES 1
Author(s) -
Montgomery Robert J.
Publication year - 1929
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1929.tb18047.x
Subject(s) - materials science , lens (geology) , refractive index , crystallization , softening point , composite material , barium , optics , softening , crown (dentistry) , thermal , mineralogy , chemistry , metallurgy , optoelectronics , physics , thermodynamics , organic chemistry
I. The process of making fused bifocal spectacle lenses is based on patents taken out about 1906. Such lenses are made by fusing a crown glass with an index of refraction of 1.5230 with a lead glass having indexes of refraction of 1.616, 1.66, and 1.69. 11. Problems in making satisfactory glass involved thermal expansion, surface crystallization, surface bubbles, and the softening temperatures of the glasses. The effect of composition of the glass in curing these defects is discussed and satisfactory compositions are given. Testing methods for control are given. III. A later development is the so‐called colorless fused bifocal in which a barium glass replaces the lead glass of the normal lens. The use of barium glass introduces new problems, especially the quality of the glass and the tarnishing of the surface. The relative softening temperatures of the barium and crown glass as well as the thermal expansion had to be controlled.