If you haven't tried to engrave stone with your Glowforge yet, I recommend this fun craft. I used Travertine Tiles (4"x4"). This natural stone is fairly soft and can be easily engraved. The unfinished surface gives it a unique and antique look. 

Paint the tiles with blue acrylic paint. I used two different shades to make them look more interesting. Once the paint has completely dried, you can place the tiles on your crumb tray.

Upload a design. I used a Mediterranean Tile Design. Resize it to fit the tiles and set the squares to "ignore". Enter the Material Thickness, in my case the tiles are 0.3". Use full speed and full power (engrave settings)

After the tiles are engraved you need to brush off the dust and seal them. I used 2 layers of Mod Podge. 

Add cork to the bottom of the tiles and let the glue dry. 

Now get yourself a glass of wine and enjoy your unique stone coasters.