NATURAL IRON OXIDE PIGMENTS -3 # Ochers

Post 408 –  by Gautam Shah 

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Ochre is an iron oxide pigment of natural and synthetic sources. Ochers are coloured soft deposit of clays often with mixed layers or pockets harder crystalline iron ore. Some of the best yellow ocher’s are mined at Roussillon, Southern France. Here the mineral formations are naturally stained with colours to provide a wide variety of earth or natural iron oxide colours.

ocher_rocks_rock_ocher_roussillon_places France

The Greek word ochros, for Ochres describes it to a pallid or pale yellow, but natural ochers are brilliant colours. Ochres have a colour range that varies from yellow to deep orange or brown, due to the hydrated iron oxide. This is unlike the Red oxide which is from hematite powder, a form of iron oxide (Fe2O3). An ochre containing a large amount of hematite has a reddish tint, and is known as ‘red ochre’. The dominant yellow colour of ochre is due to the mineral limonite. Ochres are of two kinds, one with an argillaceous or clayey basis has richer colours, whereas the other with a calcareous base is slightly of ‘flatter’ colours. The nature of the associated minerals affects the colour, such as calcareous varieties have brownish-red and dark-brown shades, and aluminous types offer red and violet tints.

Vaucluse-roussillon-village

Earth colours of Roussillon village France

Different colours of Ochre pigments are extracted from different veins, and then mixed to obtain specific shades. Other shades are created by roasting (‘burnt’ or calcination), and dehydrating the mineral clays.

Santorini_girl_picks_flowers

Yellow Ochre is a very ancient pigment. It is without any trace of green. The oxide colours are called Earth colours, due to their richness, brightness and warmth. Ochres are mixed with high refractive whites like Lime (or zinc, titanium dioxide), or low refractive ‘extenders’ such as the barytes to achieve, respectively, high opacity or translucency.

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Manuscript Cover India in Ocher colours

In Ancient Greece, red-ocher was called miltos, (hence Miltiades red-haired or ruddy). In Athens when assembly was called, everyone was supposed to attend it, and failure to attend it incurred a fine. To prevent people loitering around slaves swept the open space of the Agora with ropes dipped in miltos . It was also known as raddle, reddle or ruddle. In Ancient Egypt, the ochre was often used in place of gold, which was considered to be eternal and indestructible. It was used for painting tomb interiors in place of toxic orpiment (an orange-yellow coloured arsenic sulfide mineral). Ochre was used for painting women’s faces. Romans used the yellow ochre to to represent gold, skin tones, and as a background colour in their paintings such as the murals of Pompeii.

Egyptian Ocher colours

A rational process for refining ochre pigment was developed by the French scientist from Roussillon province of France, Jean-Étienne Astier (1780s). He washed the clay to separate the grains of sand from the particles of ochre. The decanted and dried ochre was crushed, sifted, and ground as the pigment. Best of the qualities were used for artists’ colours.

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Ochre robed Sadhus sitting on the Vishnu Temple of Kathmandu’s Durbar Square, Nepal Wikipedia Image by us Koljonen (Dilaudid)

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NATURAL IRON OXIDE PIGMENTS – 1

NATURAL IRON OXIDE PIGMENTS – 1

Post 406 ⇒   by Gautam Shah 

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Iron Oxide ColoursNatural Iron oxide pigments are some of the most commonly available colourants, nearly everywhere on earth. There are as many regional, as there are local colour variants, offering a vast palette of colours ranging from nearly black, to red, brown, etc. Natural Iron oxide pigments are very stable (chemical reactivity), sunlight fast (UV radiation), nontoxic, and remain unaffected by moisture or heat (up to 550C for red oxide and up to 105C for yellow oxides). Iron oxides are resistant to oils do not react readily with solvents.

Queen Nefertiti

Iron-oxide pigments are extracted from many different types of ores such as Hematite (reds), Goethite and Limonite (Yellow-browns), Siderite (brown-reds), and Magnetite (blacks). Red hues are attributed to hematite Fe2O3, Yellows to hydrated oxides of iron, and Browns to MnO2 or black impurities. The pigments consist of Ferrous or Ferric oxides, with impurities such as clay, silica, calcium carbonate, manganese, etc.

Iron oxide Yellow pigments are based on iron oxide hydroxides are referred to by many different names, including goethite, limonite, raw sienna, Mars yellow, yellow earth, yellow ochre, yellow iron oxide, yellow hydrated oxide and iron hydroxide pigment. Iron oxide Red pigments are based on anhydrous iron oxide, and referred to as hematite, red oxide, rust, red ochre, burnt sienna, Mars red, etc. Iron oxide brown colours are mainly based on Manganese oxide or pyrolusite are brown yellow oxide, ochre, umber, burnt umber, etc. But many colours are more known by the locations of the extraction, as seen by names such as Venetian red, Sinopia, Turkey red, Indian red, Spanish red, Pompeian red, Persian red, etc.

Lascaux

Oxide colours have retained their fascination mainly due to the stability and consistency. Red and Yellow oxides were two shades that have survived in caves for nearly 70000 of years. The advantage of red oxide offered was against the most commonly known red colour of the blood. But colour of the blood turns brown on drying and is highly susceptible to biological degradation. Blood colours are translucent and are not comparable to red of the oxide colours. Black was used in cave paintings, but its source the carbon (lamp) black offered very fast, intense and indestructible shade. Even the occasional (in few regions) use of Black iron oxide is no match for it. Black colour was also made by reacting Iron with an acidic substance. Another natural red colour was the Indian vermilion, made by reacting turmeric with an acid.

Oxide colours were used for body decoration. Pigments grinding equipment believed to be between 350,000 and 400,000 years old has been reported in a cave at Twin Rivers, near Lusaka, Zambia. The technology of refining by way of cleaning, washing, sieving and grinding, and calcining is very ancient. The naming of oxide colours as raw or burnt for ochre, umber or senna, was familiar to all artists for ages. By heating or calcining the oxide colours became intense or rich.

Namibie Himba Oxide body colour

Before the Industrial Revolution, the range of colours available for art and decorative uses were limited. The range consisted earth or mineral pigments or colours of biological origin. At places colourants from unusual sources such as botanical materials, animal waste, insects, etc. were used. The colour range was sought to be enlarged by purification, mixing with other colours and chemical treatments.

It was realized by artist that the range of hues and tones offered by Iron Oxide colours is limited. During the industrial revolution period efforts began to produce very large and consistent quantity of synthetic equivalents.

The son of a master dyer, Tintoretto used Carmine Red Lake pigment, derived from the cochineal insect, to achieve dramatic colour effects.

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