Porcelain enamel signs are made by fusing powdered glass to a substrate of low carbon steel. This is done by a firing process.. Artsign Design has capacity for up to 20 x 20 inches. Our kiln melts, flows and finally hardens under temperatures exceeding 1400°F. The outcome is a durable vitreous coating. This forms the grey base layer, which is chemically bonded to the metal. For any additional color, a separate layer of powdered glass must be applied and fired independently. By using this method, enameling produces very smooth, high-gloss finishes in a wide variety of colors.