profondeur du lustre

OBS: An unofficial numismatic term used to describe the reflective fields of proofs and prooflikes. Mirror depth can be measured by holding printed matter in front of a coin and increasing the distance between the two. If the printing is reflected in the field but is not clear at a distance of under one inch, the coin is semi-prooflike; if clearly reflected, that is readable, at a distance of one to four inches, the coin is prooflike and has a deep mirror; similarly at four to eight inches, it is very deep, and ultra deep beyond eight inches.
OBS: See related term: cameo contrast.