Spectacles
Ground glass lenses roughly double the working life of a skilled craftsman.
- When
- Known to
- ± 5 years
- Era
- Post-Classical, Holocene
Convex lenses for reading appear in northern Italy around 1286, described in a sermon by a friar who says the maker refused to share the technique. Presbyopia begins in the forties, so before spectacles a scribe, jeweller or scholar simply stopped being able to work. The economic effect of extending skilled careers by decades is easy to underrate, and the lens-grinding tradition leads directly to the telescope and microscope.