Diamond fibres have been deposited by hot-filament chemical vapour deposition on a Pt. wire of 150 mu m diameter to form a diamond fibre. These diamond fibres with a Pt core were much less brittle than corresponding W-cored diamond fibres. This is attributed to a thin graphitic layer between the core and the diamond, which allowed interface decohesion and plastic deformation of the ductile Pt core. The interface microstructure is compared with other observations on diamond-Pt interfaces. (C) Crown