What is "siderography"

Siderography \Sid`er*og"ra*phy\, n. [Gr. ??? iron + -graphy.] The art or practice of steel engraving; especially, the process, invented by Perkins, of multiplying facsimiles of an engraved steel plate by first rolling over it, when hardened, a soft steel cylinder, and then rolling the cylinder, when hardened, over a soft steel plate, which thus becomes a facsimile of the original. The process has been superseded by electrotypy.

n. A 19th-century process of reproducing steel-engraved designs for printing. The design is engraved on a steel block, then hardened and used to transfer a raised-image version to a steel roller under heavy pressure. The roller is then hardened and used as a die to impress duplicate images on printing plates for transferring to paper by the intaglio method.