The density of optical glass lies between 2.4 g/cm3 and 6.2 g/cm3. It is measured using a buoyancy force method with uncertainty better than 0.001 g/cm3. Lowindex crown glasses have lowest density. With increasing refractive index, density rises considerably (Fig. 7.1).
The replacement of classical glass types by lead- and arsenic-free glasses has led to lower density. The reduction effect increases with the lead content of the predecessor glass types and hence with its refractive index. The density reduction may amount up to 36% as with N-SF57 (3.53 g/cm3) and SF57 (5.510 g/cm3). Table 7.1 gives density values for selected classical glass types and their successor glass types. Low-index crown glasses show no effect since they were already lead free.
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