Microporous synthetic resin material

Claim 1

A STAMP FORM HAVING SUITABLE MARKINGS ON A FACE THEREOF, SAID FORM COMPRISING A MICROPOROUS MATERIAL COMPRISING INTERCONNECTED AGGREGATES OF UNITED PARTICLES OF A THERMOPLASTIC SYNTHETIC RESIN, SAID MATERIAL CONSTITUTING A SUBSTANTIALLY UNIFORM UNITARY COHESIVE RETICULAR STRUCTURE, THE AGGREGATES DEFINING A CORRESPONDING UNIFORM RETICULAR CAPILLARY PORE SYSTEM EXTENDING FROM SURFACE TO SURFACE OF THE STRUCTURE AND HAVING A FLOWABLE COLORING AGENT DISPOSED THEREIN, THE AVERAGE PERCENTAGE OF SOLID AGGREGATE MATERIAL BEING SUBSTANTIALLY THE SAME IN ANY PLANE OF THE STRUCTURE, SAID CAPILLARY PORE SYSTEM HAVING A MINIMUM AVERAGE PORE DIAMETER OF 1 MICRON AND BEING CAPABLE OF RETAINING THE COLORING AGENT DISPOSED THEREIN AND OF RELEASING THE SAME UNDER PRESSURE APPLIED TO THE RESIN BUT BEING INCAPABLE OF ABSORBING A COLORING AGENT WHICH DOES NOT WET THE RESIN.