stopping-out
Noun
Meaning
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.
Source: Webster's dictionaryExamples
This is the technique of letting the acid bite lightly over the whole plate, then stopping-out those parts of the work which the artist wishes to keep light in tone by covering them with ground before bathing the plate in acid again.
This is the technique of letting the acid dissolve lightly over the whole plate, then stopping-out those parts of the work which the artist wishes to keep shallow by covering them with ground before bathing the plate in acid again.