Ochres

Ochre
Color coordinates
Hex triplet	#CC7722
sRGBB  (r, g, b)	(204, 119, 34)
CMYKH   (c, m, y, k)	(0, 42, 83, 20)
HSV       (h, s, v)	(30°, 83%, 80%)
Source	[Unsourced]
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

Ochre (British English) (/ˈoʊkər/ OH-kər; from Greek: ὠχρός, ōkhrós, (pale yellow, pale) or ocher (American English; see spelling differences), is a natural earth pigment containing hydrated iron oxide, which ranges in colour from yellow to deep orange or brown. It is also the name of the colours produced by this pigment, especially a light brownish-yellow. A variant of ochre containing a large amount of hematite, or dehydrated iron oxide, has a reddish tint known as "red ochre" (or, in some dialects, ruddle).

Ochre is a family of earth pigments, which includes yellow ochre, red ochre, purple ochre, sienna, and umber. The major ingredient of all the ochres is iron(III) oxide-hydroxide, known as limonite, which gives them a yellow colour.

When natural sienna and umber pigments are heated, they are dehydrated and some of the limonite is transformed into hematite, giving them more reddish colours, called burnt sienna and burnt umber.

Ochres are non-toxic, and can be used to make an oil paint that dries quickly and covers surfaces thoroughly.

Modern ochre pigments often are made using synthetic iron oxide. Pigments which use natural ochre pigments indicate it with the name PY-43 (Pigment yellow 43) on the label, following the Colour Index International system.

Limonite, a mineraloid containing iron hydroxide, is the main ingredient of all the ochre pigments.

Hematite is a more reddish variety of iron oxide, and is the main ingredient of red ochre. When limonite is roasted, it turns partially to the more reddish hematite and becomes red ochre or burnt sienna.

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Wikipedia