I've gone back and forth on this challenge. Sometimes I love it and sometimes I hate it. All of the time I think there must be a better way.
The cork I bought for the coasters is about .25 inches smaller than the coaster. The ink smudges way too easily. I wasn't happy with most of the stamps I have. Then when I went to seal the ink it all ran from the Kyrlon sealer. I had to wipe it all off and start again. I don't really like the way these turned out. I'm not certain I'll try this again.
Head to your home improvement store for some ceramic tiles, and create coasters for yourself!