A method of making an impression die comprises the steps of providing a substantially planar bendable bimetal plate 10 consisting of copper and steel bonded together, forming a relief pattern 14 in the surface of the copper for example by an etching process, forming the plate into a non-planar sleeve with the copper on the outside and joining the free edges of the sleeve together. Preferably the free edges of the sleeve 10 are joined together while the sleeve is mounted on a metal mandrel 15.