"View of the vacuum chamber of Ames Laboratory's electron beam melting system. The chamber has 40+ years of use. The colors arise from oxidation across the varying thickness of metal deposits. The thick deposits consists mostly of Th, Zr, Hf, Ti and some Ni evaporated during electron beam melting.
Note: The point where the electron beam impinges on the metal being melted would be approximately at the bottom-middle of the picture. The heat-shield (foreground) protects the chamber light. You can see the shield is effective by the rainbow-shadow of ever thinning deposit layers approaching the protected lamp." by Trevor Riedemann
via ISU Photostream