A method of coating a refractory metal body consisting essentially of Mo, Ta, W or Ti, comprises the steps of (1) cleaning the body, (2) spraying molten platinum group metals (e.g. Pt, Pd, Rh, or their alloys) on to the surface, (3) plastically deforming the coating (by shotpeening, pressing or rolling), and (4) heat treating the coated body at 600-1400 DEG C. for a time sufficient to promote solid diffusion of the coating (e.g. 1-10 hours). These steps (1)-(4) are repeated until a sufficient thickness of coating metal has been built up. The heat treating step may be carried out in dry hydrogen.