Assertion: lens | /r/CapableOf | use then ground glass
Facets:
value: in polymethyl
type: OTHER
value: in the 1920s
type: TEMPORAL
value: in the 1940s
type: TEMPORAL
Source sentences:
text: Lenses would then be shaped to conform to the mould, initially using blown glass and then ground glass in the 1920s and polymethyl methacrylate in the 1940s.