This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
Ochra five Miner a ferri lutea vel rubra Pharm. Paris Ochre: an argillaceous earth; less tenacious, when moistened, than the clays and the boles; impregnated with a calx of iron, and thereby tinged of a yellow or red colour. The dark red sort is called reddle or ruddle, rubric a fabrilis the yellow fil; ochra plinio & latinis fil dicta Charleton, Those which are naturally yellow become red by burning. Both kinds are dug in several parts of England.
These earths discover their argillaceous nature, by burning hard in the fire; and their ferrugineous impregnation, by digestion in aqua regis, which extracts the iron, leaving the earth nearly white. To the taste they seem some what astringent, in consequence, not of the metallic, but of the earthy part, for the iron is in such a state as not to be acted on by any fluid that exists in the bodies of animals: it may therefore be presumed, that they do not differ materially, in virtue, from the boles; except in being less viscid, and therefore of less efficacy for obtund-ing acrid humours: see Bolus and Cimolia. Among us they are rarely or never used medicinally under their own name; though some-times applied in the shops to the counterfeiting of earths that are less common.