Embossing is the process of creating a three-imensional image or design in paper and other ductile materials. It is typically accomplished with a combination of heat and pressure on the paper. This is achieved by using a metal die (female) usually made of brass and a counter die (male) that fit together and actually squeeze the fibers of the substrate. This pressure and a combination of heat actually "irons" while raising the level of the image higher than the substrate to make it smooth. In printing this is accomplished on a letterpress. The most common machines are the Kluge Letterpress and the Heidelberg Letterpress. The term "impressing" enables one to distinguish an image lowered into the surface of a material, in distinction to an image raised out of the surface of a material. Both are "embossing" per se. For embossing metal, see repoussé.