Cymbals are very loud. This can be a problem if you want to play your drums anywhere other than in an abandoned warehouse next to the old railroad tracks. (Where, of course, you are easy prey for bad slasher flick style psycho killers.)
There is, however, a solution!
Take a piece of 2-inch wide elastic (to be found at your local haberdasher/fabric store), of a length equal to twice the diameter of your cymbal, plus about 2 inches of overlap. (E.g., for a 16" crash, use a piece 34" long.) Use pinking shears to trim the ends of the elastic to stop them unravelling. Now, make the elastic into a simple band, and sew it together.
Stretch this band around the rim of your cymbal. The band should wrap tightly around the perimeter. The whole point of this is to dampen down the vibrations of the cymbal at the rim, as this freely vibrating edge is where the bulk of the sound comes from.
To quieten down your hi-hat, you only need wrap a band around the upper cymbal. You rarely hit the bottom cymbal directly anyway, and when the two cymbals come together, the band around the top one will muffle the bottom one as well.
Cymbals muffled in this way are--astonishingly--about as loud as plastic practice cymbals. And you retain the weight and feel of playing on proper cymbals. They are the perfect accompaniment to muffle heads on your drums, if you want to practice in your house or apartment without being lynched by your neighbours.