Aluminum Arc Spheres and Iron Welding Spheres

The Aluminum arc spheres are the larger gray spheres and the black spheres are magnetite from the iron welding. The Aluminum arc spheres appear gray because they are coated with a layer of aluminum oxide, an efficient light scatterer. These spheres were formed in the inert atmosphere of the bushing. If the aluminum was formed outside the inert welding environment it would oxidize into a high refractive index colorless glass sphere. The iron weld sphere is a magnetite sphere, typical of contaminants introduce during the assembly of the bushing.