Glass on Metal - Vol. 10 - No. 1 When firing lead free transparent clears direct on copper, the firing must be sufficient for the enamel to absorb the copper oxide. This may take two to three firings at 1450 for 2 minutes. The edge of the piece should be cleaned with a file or alundum stone after each firing. This firing process is also necessary when firing transparent colors direct on copper. LAYERING Transparent Lead Free Enamels The lead free transparent pallet can be expanded by layering one color on top of another. For instance, to obtain variations of olive colors, transparent greens such as 2335 Peacock, 2340 Glass, or 2350 Grass are fired first. Then by applying a second layer (on top of the green) of 2210 Egg or 2215 Soft and firing, an olive transparent color is obtained. Another combination could be firing 2910 Elan Gray first and then layering on of the transparent blues on top resulting in a blue-gray transparent. Another way to expand the transparent pallet is to physically mix two transparent colors. Any proportion of two colors can be run through a sieve a number of times and used as is (this may result in a spotted texture color) or the two colors ca be mixed by placing them on a sheet of paper and lifting up and rolling over opposite corners of the paper until the dry enamel is uniformly mixed. For a purer color the mixture can be fired on mica or Thompson's furnace floor blanket and then re-ground with a mortar and pestle. If using mica, any residue mica should be ground off the glass frit with an alundum stone, before grinding in a mortar and pestle. if using the floor blanket, a damp cloth will remove residue fibers on the bottom of the glass frit.