This section is from the book "Chromatography; Or, A Treatise On Colours And Pigments, And Of Their Powers In Painting", by George Field. Also available from Amazon: Chromatography, or A Treatise on Colours and Pigments, and of Their Powers in Painting.
Yellow Ochre, called also Mineral yellow, is a native pigment, found in most countries, and abundantly in our own. It varies considerably in constitution and colour, in which latter particular it is found from a bright but not very vivid yellow to a brown yellow, called spruce ochre, and is always of a warm cast. Its natural variety is much increased by artificial dressing and compounding. The best yellow ochres are not powerful, hut as far as they go are valuable pigments, particularly in fresco and distemper, being neither subject to change by ordinary light, nor much affected by impure air or the action of lime; by time, however, and the direct rays of the sun they are somewhat darkened, and by burning are converted into light reds. They are among the most antient of pigments, may all be produced artificially in endless variety as they exist in nature, and iron is the principal colouring matter in them all. The following are the principal species, but they are often confounded: -
Oxford Ochre is a native pigment from the neighbourhood of Oxford, semi-opaque, of a warm yellow colour and soft argillaceous texture, absorbent of water and oil, in both which it may be used with safety according to the general character of yellow ochres, of which it is one of the best. Similar ochres are found in the Isle of Wight, in the neighbourhood of Bordeaux, and various other places.
Stone Ochre has been confounded with the above, which it frequently resembles, as it does also Roman ochre. True stone ochres are found in balls or globular masses of various sizes in the solid body of stones, lying near the surface of rocks among the quarries in Gloucestershire and elsewhere. These balls are of a smooth compact texture, in general free from grit, and of a powdery fracture. They vary exceedingly in colour, from yellow to brown, murrey, and grey, but do not differ in other respects from the preceding, and may be safely used in oil or water in the several modes of painting, and for browns and dull reds in enamel.
Dl Palito is a light yellow ochre, not differing much from the foregoing, but affording tints rather purer in colour than the brightest of them, but less so than Naples yellow. Many pleasing varieties of ochrous colours are produced by burning and compounding with lighter, brighter, and darker colours, but often very injudiciously, and adversely to that simple economy of the palette which is favourable to the certainty of operation, effect, and durability.
Roman Ochre is rather deeper and more powerful in colour than the above, but in other respects differs not essentially from them: - a remark which applies equally to yellow ochres of other denominations.
Brown Ochre, Spruce Ochre, Or Ocre De Rue, is a dark-coloured yellow ochre, in no other respects differing from the preceding: - it is much employed, and affords useful and permanent tints. This and all natural ochres require grinding and washing over to separate them from extraneous substances, and they acquire depth and redness by burning.