Etched designs are produced through the use of acid. A coating (or resist) is applied and a design cut into it. When acid is applied it only works on the exposed metal not on the coating. When the coating is removed the etched design remains.

This large oval Antique silver locket is etched with a maritime and fauna motif in a Japonesque style. Silver beads dot around the locket to create a frame. The locket drops from a 21 inch intricate silver chain.
Image courtesy of Lang Antiques