A block piece for holding a spectacle lens blank has a basic body with a workpiece mounting face portion against which the workpiece can be blocked with a blocking material, and a clamping portion via which the blocked workpiece can be fixed in a machine/apparatus for processing it. The basic body is made substantially of a material having a defined low water absorption and/or is sealed to at least reduce outgassing of water moisture under vacuum conditions, so that the block piece can be used also in vacuum coating processes. Alternatively or in addition, the clamping portion is constructed to be clamped by forces directed essentially perpendicular to the radial direction to cancel out each other and not deform the basic body, and/or the workpiece mounting face portion is provided with a predetermined amount of prism.