Assertion: early lens | /r/MadeOf | crystal
Facets:
value: sometimes
type: TEMPORAL
Source sentences:
text: Early lenses were sometimes made from crystals; one of the oldest known, the Nimrud lens in the British Museum in London, is a piece of quartz (sometimes called "rock crystal") estimated to be 3000 years old and believed to have been used as a magnifying or burning glass, though its optical quality was very poor.
text: Early lenses were sometimes made from crystals; one of the oldest known, the Nimrud lens in the British Museum in London, is a piece of quartz (sometimes called "rock crystal") estimated to be 3000 years old and believed to have been used as a magnifying or burning glass, though its optical quality was very poor.