The surface of a metal block made of an aluminium alloy is covered with narrow perpendicular grooves, which thus form an array of quadrangular pyramids touching base to base. The surface is further provided with a marker which assures the positioning of the master plate and the replica plate. Replicas prepared using this block are of higher quality than those using the velveteen-covered cylinder. A single master plate will provide ten or more replicas of good quality, the master plate being preserved for further work. Last but not least, the all-metal block can be easily cleaned and heat-sterilized.