Hi Ivan,
Soak it in 50 percent Clorox solution over night and the clean using a little
rotary drill with a file like tool chucked up. The clorox loosens the stuff so
that it will normally flake off when bumped with the rotating tool. You can
also do the job with a dental hand tool. If it don't come off very easy, soak
it another night.
Bud Rogers
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