The Collaborative International Dictionary
Stopping-out
Stopping-out \Stop"ping-out`\, n. A method adopted in etching, to keep the acid from those parts which are already sufficiently corroded, by applying varnish or other covering matter with a brush, but allowing the acid to act on the other parts.
Wiktionary
stopping-out
n. An etching technique used to keep the acid from those parts which are already sufficiently corroded by applying varnish or other covering matter with a brush, but allowing the acid to act on the other parts.