These are coasters I've been making for some of my workshops lately and they really are proving popular. People get really excited when they see that the designs are actually paper napkins (don't we all love those) and I have simply glued them on.
The idea is really simple, just grab a few unglazed stone tiles and brush them well with Mod Podge. Take a paper napkin and cut it into four. Peel off the two backing layers of the napkin and apply the design to the surface of the tile. Leave them overnight to dry then sand the edges with a foam sanding pad before varnishing. Oh and I also stick on some clear bumps underneath to protect my tables.