Orcs: Characteristics (p3)

Orcs made no beautiful things, but many clever ones including machines, tools, weapons, and instruments of torture. They were delighted by wheels, engines, and explosions, and could tunnel and mine as well as any but the most skilled Dwarves, though they are often untidy and dirty.[3] This was so since the time Melkor bred them (in an unknown process) from mutilated and corrupted Elves. They hated themselves, and had an even deeper secret hatred for Melkor, thus resulting as a violent and warlike race in a perpetual state of chaos with itself and others. Despite their abominable nature, Orcs were often crafty and clever rather than dim-witted. Tolkien writes that they were capable smiths and craftsmen, though their weapons and belongings are described as crude compared to those of the Free Peoples. Orcs also developed tunnel-making, so as to dwell underground away from the light.