how would you go about cleaning dielectric from a blown ceramic capacitor?

the dielectric is white.

also i'm having some trouble identifying the capacitance. they are blue ceramic hi voltage capacitors that say:

472M
250V ~ x1y1
400V~C

and
102M
250V ~ x1y1
400V~C

I read on a different post that the letter is sometimes used to indicate the tolerance? for instance
27J 3kV would be a 27pF with 5% tolerance