Choose the size of mosaic that you wish to create. If you want the light to come through the glass, start with a piece of clear glass as your base. The bigger your panel, the thicker the glass should be. If your panels is larger than 2 ft. by 2 1/2 ft. you must consider using tempered glass. Carefully choose the colors of glass that you want in the mosaic. You can find stained glass online or at an art glass merchant (I prefer to see all of my choices in the store that way you can see the true color of the glass).