How perfect is perfect? Somebody can consider that a 1/32" accuracy is
perfect enough whil another isn't happy with an accuracy of a 1/4 wavelength
of green light.
Making a sphere isn't a hard chore at all. Rubbing another piece of
material over the surface will quickly produce a spherical surface to the
size of the grit used and gradually to a fair bit more accurate than that.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works evevery time it is tried!