silver film

https://doi.org/10.1351/goldbook.S05672
When viewed in reflected white light against a black background, transparent films show the classical interference colours of thin plates which permit an estimate of their thickness to be made. When of the order of \(100\ \text{nm}\) (\(1000\ \unicode{x212B}\)) in thickness they appear white (silver @[email protected]) and when thinner they appear gradually less intensely white, then grey and finally black.
Source:
PAC, 1972, 31, 577. (Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry) on page 614 [Terms] [Paper]