Applying a diamond layer onto a graphite substrate by a chemical vapor deposition (CVD) process, involves subjecting the graphite substrate to the pretreatment steps before the CVD process. The pretreatment involves fine cleaning of the surface in a vacuum at a temperature of greater than 500 (preferably greater than 800)[deg] C, in an etching gas atmosphere, mechanical removal of loose particles, seeding of the substrate surface with very small diamond particles, and at least one degassing treatment in a vacuum to remove adsorbed hydrocarbons and adsorbed air at a temperature of greater than 500 (preferably greater than 700)[deg] C.