Annealing (metallurgy) brass can be cooled slowly in air, or quickly by quenching in water, unlike ferrous metals, such as steel, which must be cooled slowly to anneal. In this fashion, the metal is softened and prepared for further work—such as shaping, stamping, or forming. Annealing occurs by the diffusion of atoms within a solid material, so that the material progresses towards its equilibrium state. Heat increases the rate of diffusion by providing the energy needed to break bonds. The movement of atoms has the effect of redistributing and eradicating the dislocations in metals and (to a lesser extent) in ceramics. This
Glass-to-metal seal directly sealed to lead glass, as it reacts with the lead oxide and reduces it to metallic lead. For sealing to lead glasses, it has to be copper-plated or an intermediate lead-free glass has to be used. Iron is prone to creating gas bubbles in glass due to the residual carbon impurities; these can be removed by heating in wet hydrogen. Plating with copper, nickel or chromium is also advised. Chromium is a highly reactive metal present in many iron alloys. Chromium may react with glass, reducing the silicon and forming crystals of chromium silicide growing into the glass and