These coasters are made out of slate, so the have the natural edges, and may change a bit on the thickness.  The have a non-marring rubber feet, so they are safe to use on any surface without worrying about marring the table, etc. We can actually engrave these with anything you like, just Email CrownPC@yahoo.com with your idea and we can verify the order before you pay for it. 4"x4" in size in natural slate, so your glasses sweat will be absorbed by the slate, and slowly evaporate into the air. Each order consists of 4 coasters. Cheaper than all of our competitors, and engraved right here in our own print shop.