[ATM] problem with mirror blank

[horace r davis]

i have the 16 inch porthole the mirror glass not the same quality as new
blank of pirex
the tool and mirror are mated and i have reached .200 inch in center
i am getting very close to a small imperfection in the blank i am at .120
grit know.
if i hit it do i need to grind through and problem remove at least .02
from the entire mirror
or can i have the mirror coated and just cover it up with black paint or
some thing I don't think it is over .025 in dia
would like your impute