Start your design   Sketch your design on the pot, indicating where you want certain sections of color or specific patterns. Wearing gloves and using the plastic knife, spread a 1/4-inch layer of thin-set mortar over the first section of your design. (For larger projects, use a notched mortar trowel to spread the mortar.) Do one area at a time; the mortar will begin to harden in 15 minutes. Press mosaic pieces into the wet mortar, spacing them about 1/4 inch apart. Repeat with remaining…