There were just several discussions about stamping on glazed tiles. It sounds like if you stick them in the microwave for about 30 seconds the stazon will set and then you can color. BUT since they are glazed tiles (made to be waterproof), the stazon can be washed off with soap and water. So, if you are doing 2" x 2" fidge magnets (that wont be washed) you are good to go with the nuking. If you are doing coasters, you should switch to tumbled tiles instead.
Annette
http://stamponthis.com