Place your quarter inside of the napkin.
Crumple up the napkin so that the quarter is wrapped inside of it.
Hold the can of butane upside down. Holding the napkin-wrapped quarter in your other hand, press the nozzle of the butane canister into the napkin for a few seconds.
Set down the can of butane and blow onto the napkin. You should see vapor coming off of the napkin because of the difference in temperatures.
Unwrap the napkin to reveal a frosty coin.