We usually deal with tiles made from granite or marble, which have a highly polished surface and have also often been treated with fillers as their matrix leave holes in the surface after being cut. The fillers do fill these holes and cracks to make the surface even. Sometimes this affects how well your stencil sticks to the surface. These tiles also have a matrix consisting of at least two different colors, which make it almost mandatory to think about color-filling the blasted areas to make the design or text readable.
With these stone tiles, you want to choose the thicker version of your photoresist product because you have to blast longer to achieve depth. The depth is also necessary for the paint to be below the surface to protect it from being scrubbed while cleaning. You will blast these at about 40 pounds of pressure and hold your nozzle about 10″ from the surface.
-Ruth Dobbins, Professional Glass Consultants