Improved razors and razor blades and processes for producing razor blades (16, 20, 44) or similar cutting tools with sharp and durable cutting edges, by hard-carbon coating of blades with amorphous diamond, preferably using a filtered cathodic arc plasma source. A coating of amorphous diamond (60) having at least 40 percent sp3 carbon bonding, a hardness of at least 45 gigapascals and a modulus of at least 400 gigapascals is applied to the sharpened edge of a substrate (50). The substrate may be mechanically honed, and there is no interlayer between the substrate and the amorphous diamond coating. The coating imparts stiffness and rigidity to a thin blade while maintaining a high aspect ratio.