To make numbered drinking glasses you'll need nontoxic glass paint (such as Pebeo Vitrea 160, available at crafts stores in assorted colors), a fine-point paintbrush, self-adhesive shelf liner (available at hardware stores), and a utility knife, in addition to your collection of glasses.
1. In a word-processing program on your computer, choose an attractive, boldface font and type numerals 1 to 8 (or however many glasses you will be decorating), spacing characters about an inch apart. Size the numerals in proportion to your glasses (ours were about 3/4 inch tall); print the document.
2. On a copy machine, choose the mirror image function on the control panel, and copy the document.
3. Place self-adhesive shelf liner over the reversed image; trace around each of the numerals with a ballpoint pen. Cut out numbers from shelf liner, leaving empty space around each one.
4. Peel the backing off one of the numbers, and carefully adhere it to the outside of a glass, just under its lip. Cut out the number by using the tip of a utility knife to trim carefully around the traced outline. Peel off the numeral portion of the shelf liner, leaving a "negative" of the image on the glass.
5. With a fine-point paintbrush, fill in the empty space with a coat of glass paint; the amount of paint you use will determine how opaque the numeral appears on the glass. Immediately peel off the remaining contact paper from the glass, being careful not to smudge the paint. Repeat with other numerals and glasses. Let dry for 24 hours.
6. Place all glasses upside down on a baking sheet, and bake them in your oven according to the instructions on the paint bottle. Cool glasses thoroughly before handling. The paint is dishwasher- and microwave-safe.