Abstract: Aqueous chemical milling solutions for aluminum and aluminum alloys. These solutions contain a caustic; a nitrate or nitrite; and, optionally, a diol or polyol such as ethylene glycol or glycerin. Chemical milling processes which employ such solutions.

Abstract: Optical workpiece viewing systsms and associated apparatus for electron beam welders and other workpiece processing machines which generate metal vapors. The subject systems have replaceable shields which keep the optical components of the system from being coated by condensation of vapors generated during the welding operation, and the associated apparatus includes an arrangement for changing shields as they become clouded which reduces to a small fraction the time conventionally required for that purpose. Workpiece processing machines with optical viewing system and related apparatus of the character just described.