Discs of clear glass ground on a wheel and polished with fine abrasive until they magnify without distorting — the most exacting work a glassworker does, and priced accordingly. A good lens takes days of grinding and testing, and a slip at the end wastes all of it. Scribes and the failing-sighted prize them; so do those who wish to look closely at things too small to see.
Lenses
Ground and polished glass lenses for magnification; costly and fragile.