PATINA, a name given to the rust or asrugo of coins and medals. Pinkerton (Essay on Medals, edit. 1789, vol. i., p. I6J) says, 'nothing contributes so much to the conser7ation of brass or copper coins as that fine rust, appearing like varmsh, which their lying in a particular soil occasions. Cold admits no rust but iron mould, when lying in a soil .mpregnated with iron. Silver takes many kinds, but chielly green and red, which yield to vinegar. For in gold and silver the rust is prejudicial, and to be removed; whereas ji brass and copper it is preservative and ornamental: a circumstance re-.narked by the anneals, as the ' pocula ado randrc rubiginis' of Juvenal mar prove, and that exq.u.'« Greek phrase which terms pulina x"^*°" apjoe. "the ttymrr of brass.' This fine rust, which is indeed a natural i »r;u»i. not mutable by any power of human art, is sometime* a delicate blue, like that of a tuiquoiso, sometime* of a Xtrjijjc brown, equal to that observable in antient statue* of ur-cj*. and so highly prized; and sometimes of an exquu:le grcrx a little on the azure hue, which lost is the most lx-»ui,l_ I all. It is also found of a fine purple, uf olive, and of a eras colour, or pale yellow: which last is exquisite, and abava \im impression to as much advantage as paper uf cream co. j..-. used in all great foreign presses, docs copper-plain »j,i printing. The Neapolitan palina is of a light grern; «_■!. when free from excrescence or blemish, is. very beauiifuL Sometimes the purple patina gleams through au upr«r cuji of another colour, with as lino effect as a varicgaled wJk at gem. In a few instances a rust of deeper green a found; and it is sometimes spoiled with the red ur bmr.j* made, which gives it quite the appearance of the East L>i_i;i »^jne called blood-stone. These rusts are all, when the icai production of time, as hard as the metal itsolf, anil (.cmus a much heller than any artificial varnish could have aaaa. concealing at the same time not the most minute parucltaf the impression of the coin.'
Note - this article incorporates content from The Penny Cyclopaedia of the Society for the Diffusion of Useful Knowledge (1840)