- Colorific Earth. Kirw. 1. 194.
- Yellow Earth. Ditto.
- Gelberde. Werner.
Having figured the Yellow as well as Red Earths, and mixtures of Iron with Clay, &c., commonly called Ochres, I venture to consider it as not very irregular, being in some degree natural, to exhibit the following varieties. These may, from their texture and nature, arrange with or near the former, and so complete the list of colours, as they altogether seem to be mostly regarded in that light; and it may serve as an example for the order of other substances, when they have any thing lo do with colours, as to arrangement.—Thus I would place the lightest first, and as regularly as I could, the primitives, and then those derived from them. I have, in tab. 10, considered the light blue Iron Ore, merely as such, as it has little or no Earth but what may be considered as adventitious; and it might claim a place hereabouts, from its resemblance to a loose Ochre, and may seem necessary to help the purples on this plate. As purples*, dark browns, and nearly blacks, have scarcely yet been noticed, this may become instructive, as it is curious and natural. Whether the purples depend upon the same mixture as in the Clay—lower fig, tab. 252—I do not know.
The upper figured specimen came from the Isle of Wight; I was favoured with it by my botanical friend C. Lyell, Esq., and I have some from Wales nearly of the same tint, by favour of Lady Wilson. The darker ones I have received from various persons and places; and as they are really interesting, I shall be the more particular concerning them. It would appear, by the experience of Klaproth, that the blue Iron Ores, commonly so called, are the effects of Phosphorus; although Mr. Kirwan doubted it, as I have observed at tab. 10. The darker blue Iron Ore, called Native Prussian Blue, from North Wales, which I had with Mr. Day’s collection, and also by favour of a friend, from near Aberdeen, are more solid, and darker, than that figured, and will serve to fill up the arrangement. I believe them to be nearly the same as to the colouring ingredients; this being more mixed with a darkish Clay, which gives it the appearance of Indigo Blue. Thus we see the three primitive tints may be found in Ochres, and more or less in the Clays, as some of the Welsh specimens have rather more Clay than others, although not worth a different specification; and the whole serves an important purpose, viz. to satisfy us pretty nearly as to what may be expected from coloured Clays, or Ochres, as I show the brightest I have seen of them.
That they may be mixed to form greens may sometimes happen in nature; but I have only seen it so in Clay, as mentioned and figured tab. 247. Greens seem more combined in another way, as with Chlorite, Terre-vert, or Talc, as tab. 182, lower fig., and among the precious stones the Emerald is green, which is said to be caused by Oxide of Chrome.
Colours are only brilliant by means of the substance which reflects them, as I shall show in my New Arrangement of Colours.
Brown Earths are called Umbers; but are very much allied in their nature to the Ochres. Thus they may, with some regularity, be placed near them in this instance. Common Umber of the shops is of this kind, and will bum darker; hence we have raw and burnt Umber. Clayey Iron Stones often approach the appearance of the Umber used by painters, of which the best is said to come from the Levant. I have three or more varieties, including a substance much related to it, and Cullen’s Earthy as it is called in the shops, originally brought from Cologne in Germany.
The second or middle figure in the plate is such as is sometimes found in the hollows of Quartzose rocks in moderate quantities. I have it from Devonshire, by favour of Colonel Montague, It seems to be an Oxide of Iron with the carbonaceous remains of vegetables.
The next right hand figure was sent me from Scotland; I have some also from Warwickshire, by favour of Lady Markham, found among the Ruddle. The Iron in most of them blackens when heated, and becomes magnetic, particularly in this last, and the vegetable remains are affected, something like Touchwood—see the left hand darker powdery figure. A more vegetable substance still is that resembling Colonian Earth, which I have along with petrified Wood and Jet, The form of the Wood remains represented in Stone, chiefly Quartzosc, &c.; the Bitumen in the form of Jet, and the real Wood is as it were displaced in this earthy form. This more than commonly interesting specimen was sent from Kettleness near Whitby in Yorkshire, by favour of J. M. Sowerby, Esq.
The lower figure represents Terra Siennæ, a famous rich brown; chiefly an oxygenized Iron, It was sent by Nathaniel John Winch, Esq. and his friend Thomas Crawhall, Esq. from Cheviot Hills. It is certainly a new addition to the mineralogical catalogue of Great Britain, It is generally found in small pieces, is brittle, and often with a sharpish and smooth or glossy conchoidal fracture, having occasionally loose grains of yellowish Ochre about it. It may be used in a more transparent style than those before mentioned, and will serve in the last spirited touch, to give a zest to the picture, and leaves it in the highest taste, especially suited to Rembrandt’s style, Asphaltum, v. 2. p. 74, occasionally supersedes the use of this; and that from Egypt is preferred: not but we have it as good, though not so plentiful — see tab. 139.
Thus we have a means of mixing all possible tints in a common earthy form well suited for earthy representations, viz. landscapes, and they have very fairly obtained their proper places in the hands of artists of that class.
- * Iron is understood to have but two sorts of Oxicta, the black, or martial Ethiops, and the red, any other colour or tint b ting- produced by a particular mixture.