Lenses for eyeglasses are first mass-produced in Venice in
about 1275. Porta gives the first description of the process in
Magiae Naturalis” (1588), which differs little in principal from
that generally used up to 1915.
Porta uses the term pilae vitreae to designate the cylinders of
glass from which sections are sliced with a diamond cutter
and are sent from Germany to Venice for polishing. This is the
term (hollow balls, filled with water) used by to describe
magnifiers in antiquity.