How to Fire Porcelain on Metal

Oven interiors are coated with easy-to-clean, baked-on porcelain.

Porcelain coating over metal is used in appliances, industrial applications and handmade jewelry. Because the colors are vivid and durable, this finish creates one of the most economical and color-durable metal finishes available. Powder-coated surfaces are more resistant to chipping, scratches and fading than painted enamels. Because the finishes are UV-resistant, colors stay brighter for longer periods of time.

Things You'll Need

• High temperature-resistant metal filler, liquid metal or solder
• Metal degreaser
• Porcelain base coat
• Porcelain top coat
• Low-pressure application gun
• High temperature curing oven
• Safety equipment, including gloves, respirator, coveralls and goggles

Instructions

1. Degrease the metal surface of any manufacturing residue. Petroleum products are used during the manufacturing process to cool machinery and to help the metals release from molds. These residues must be removed. Otherwise, the porcelain coating will not stick to the metal surface.

2. Fill any casting imperfections if you are working with cast metal objects. When working with cast metal figurines or artwork, any pits in the surface should be filled with a liquid metal, and casting flashing should be filed off the object. (For rolled sheet steel, this doesn't apply.)

3. Apply the ground coat, which is also called the primer coat, with a low-pressure porcelain coating paint gun. The spray gun applies the ground coat quickly and evenly, preparing the item for its first firing.

4. Heat the coated metal in a temperature-controlled furnace. For the first firing, typical parameters include heating the item at 980 degrees Fahrenheit for 10 minutes. These parameters may change based on the type of steel and the paints used. Check the coating manufacturer's instructions for details.

5. Apply a second coat with the spray gun to the hot primed metal object. The second coat adheres to the object because of its elevated temperature.

6. Complete the project by firing the metal item a second time at 1000 degrees Fahrenheit for one to two minutes. Because of the difference between the two coatings and the elevated starting temperature of the primed metal, the second firing is much shorter than the first.

Tips & Warnings

• Some porcelain finishing systems require one coat, while other systems require two coats of porcelain finish. The differences between the systems depends on the quality of the steel and the product's end use.

References

• AK Steel: Enameling Steels
• U.S. Steel: Vitreous Enamel Sheet
• International Enamelers Congress; Porcelain Enamels for Sanitary Ware; Alain Aronica