What does "siderography" mean?

Siderography: 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 The process has been superseded by electrotypy.