Prints made by the "steel engraving (printing process)," in which plates of steel or steel-faced copper are used, having replaced the use of less durable copper plates in the early 19th century. Steel engraving was introduced in 1792 by Jacob Perkins, an American inventor, originally for banknote printing. They are often distinguished by the use of engraving, etching, and the roulette. For documents produced in long runs with precise replication, use "siderographs."
