Your correct on the glass beading recommendation. I am not a fan of this. I have see the beads wedge themselves in between the porcelain and body. Only removing them with a small pick will work. Who knows what would have happened if the beads where not discovered. An alternative is to buy some carb cleaner. Spray some into a glass jar and immerse the plugs electrode area into the fluid. I usually close the jar and leave it over night. Plugs should come out really clean.

Garth