One chipped glass can ruin an entire set, especially when you regularly use all of your glasses. But for the accident prone, a chipped glass is almost a certain eventuality. In repairing one, you have two choices--replace the missing piece or polish the rim to make the glass safe for handling.
Check your glass to make sure it has no insulating seal. If it does not, go on to the next step. If it does, fixing your chipped glass may be impossible while retaining its insulation, so you may have to simply buy a new glass.
Search for the missing piece. If it cannot be found, move on to Step 4. If you can find it, cement it back into place using a small amount of cellulose cement or epoxy. The piece must stay in place for several hours in order to completely dry, so position the cup in a manner by which you do not have to hold it.
Wet the surface of the glass, and rub a piece of silicon carbide cloth along any rough edges. Although the chip will still be a visible defect, the glass is now safe for use.
Wet the glass, if the chipped piece cannot be found, and slide the silicon carbide cloth along chipped edge. This will make the glass safe for use.