How I get them really clean, inside and out. First I make a paste of tin oxide and water. This is applied to the outside of an insulator that has been pre - cleaned. Then I carefully buff it with a 3 inch buff on the machine you see here. (This machine set up is made for polishing dentures in a dental lab.) Next I slurry, then buff the inside thread area with the spindle that's in the lathe in the picture. I made this by cutting a slot, lengthwise about 1.5", in a large nail. Through the slot I placed a 1" strip of soft cloth, which winds up as the spindle spins.