An electrotype has a thin copper shell deposited by electrolysis onto the letterpress type. The copper coating is more durable than the original type metal and the thin covering makes for a sharper and more accurate printing surface than a stereotype with its intermediate step of a mould. Invented in Russia in 1838 by Moritz von Jacobi (according to most sources) electrotyping was used for over a century in printing longer, high quality runs.

The basic chemistry of the process can be seen in this Met video of a Tiffany vase being duplicated by electrolysis.