I agree with Bob May, but would like to add a few suggestions, first make sure your mirror is
completely polished out, polishing will progress
from the center and gradually expand out to the edge, you will notice when reflecting sunlight,a
hazy "graininess" around the edge, continue poli
shing until this is gone, when polishing with lap
on top of mirror do not! extend lap too far over edge of mirror or you will "roll"(turn down) the
edge.
Remember to press frequently, good contact is
very important, press for about 10 minutes,polish
10 minutes, if it starts to dry out, spray some
water on lap(plastic water bottle sprayer is essential).
use slow and somewhat randomized 1/3 diameter,
center over center strokes(for polishing out to
sphere), with light to medium pressure.
There is no set number of strokes to parabolize
a particular diameter mirror, to parabolize center
mirror on top of lap,(with no weight on mirror),
press for 2-3 minutes,then use the "W" stroke for about 2 minutes rotating mirror slightly at the end of each excursion, then test mirror,(initially
you may do 2 or 3, 2-min press/parabolizing cycles
but as you get closer to perfection the mirror should be tested after every 1 or 2 minute parabolizing cycle, by minimizing the parabolizing
cycle times you reduce the risk of overcorrecting.