Ochre is a natural earth containing silica and clay tinted by hydrous forms of iron oxide, such as yellow-brown limonite or brown-yellow to green-yellow goethite, and traces of gypsum or manganese carbonate. Limonite is a general term used to describe all forms of hydrated iron oxide minerals (FeO(OH)) that occur as natural clay or earth. Limonite includes the minerals goethite, akaganeite and lepidocrocite. To be considered an ochre, the content of iron oxide must not be less than 12%. Depending upon the content of hydrated iron oxide, the color of ochre varies from light yellow to golden to orange. The higher the content of iron oxide in an ochre the greater its tinting strength and hiding power. Most yellow ochres are normally not calcined as heat does relatively little to alter their color. Like red iron oxides (hematite), they are found around the world and have been used as pigments since prehistory. Depending upon the colour, the ochres are called red ochre, yellow ochre, green earths, sienna, umber and by various other names. In addition to red ochre, the red oxide of iron, commonly called 'red oxide', is an important natural pigment. It results from the alteration of hematite and ferruginous laterite and consists essentially of Fe2O3 having pigmentary quality .
Properties
The staining power, brilliance and fineness of texture are the main properties by which an ochre is judged for its quality and value in industry. The tint should be wholly of the inorganic ingredient.
The principal use of ochre is as tinting colours. It is used for colour washes, distemper and oil paints. It is also used in making coloured paper. For this particular use ochre and china-clay or soapstone, after dissolving in water in paste form, are acreened and added in the beater for the prepareation of coloured paper pulp. Red oxide pigments are widely used as primers for painting structural steel, automobile bodies, ship bottoms, etc. Red ochre Powder is also a important constituent of a number of abrasives and pigments.
Paint
Used in every type of paint, primer, powder, coating etc.
Cement Industry
One of the important raw material in manufacturing of Clinker.
Tiles & Ceramic Industry
Plastic & Rubber
Fertilizer
Yellow Ochre
Yellow ochre, is a form on hydrated iron(III) hydroxide (FeO(OH) • nH2O). It's usually called limonite but limonite is not a true mineral name (although it's commonly used by geologists). Limonite is actually a mixture of different iron hydroxide minerals which typically form when iron-rich water encounters atmospheric oxygen (and typically helped along by Fe-fixing bacteria) - hence the name "bog iron" for sedimentary deposits of this mineral.
Red Ochre
Red ochre is derived from hematite (Fe2O3) which is oxidized iron and rusty red in color (rust and hematite are essentially the same thing). The name hematite comes from αἷμα (haima) the Greek word for blood (same root as hemoglobin) because of the color. Red oxide usually contains about 70% Fe2O3
Sienna
SiennaSienna is a brownish yellow containing about 60% Fe2O3 with some quantity of manganese oxide. It is named after sthe town of Sienna in Italy where a large deposit is located. Sienna is marketed in the raw and burnt (calcined) states.
Umber
Umber is a natural brown or reddish-brown earth pigment that contains iron oxide and manganese oxide. It is darker than the other similar earth pigments, ochre and sienna. In its natural form, it is called raw umber. When heated (calcined), the color becomes more intense, and the color is known as Burnt umber.
