Italian Dark Ocher is a natural brown iron oxide mineral (goethite) from quarries in northern Italy. It has a dark reddish brown in mass tone and yellowish brown tints and washes that are semi-transparent. It has two major characteristics: it never fades in daylight and the color is concentrated.
|Common Names:||English: dark ocher |
French: ocre foncé
German: Ocker dunkel
Italian: ocra scuro
Spanish: ocre obscuro
|Synonyms:||Goethite, limonite, raw sienna, yellow earth, yellow ocher, yellow iron oxide, yellow hydrated oxide and iron hydroxide pigment|
|Alternate Name:||Mars yellow is the name given to the synthetic form of yellow iron oxide hydroxide.|
Origin and History
Known since the antiquity, ocher (okhra in Greek) occurs naturally as yellow ocher () or as red ocher (). Brown ocher is a mixture of the two minerals and often manganese oxides, resulting in varying degrees of brown from yellow to red. Ocher has been used as a pigment since prehistoric times and is perhaps the most widely used pigment for artists paints.
Brown ocher is a natural earth containing clay tinted by iron oxide and is composed of the mineral and clay with traces of quartz, gypsum, manganese carbonate and other accessory minerals. Historically, ocher was designated by the mineral name limonite. Limonite, however, is not a true mineral, but a general term used to describe all forms of hydrated iron oxide minerals (α-FeOOH) that occur as natural earth. Limonite includes the minerals , akaganeite and lepidocrocite. The names for iron oxide pigments are confusing. The names earth and ocher are suitable when it is clear that the pigment comes from a natural source. Earth is a more general term, since ocher refers to a specific type of iron oxide deposit containing kaolin (clay) and quartz. To be considered an ocher, for example, the content of iron oxide must not be less than 12%. Depending upon the content of hydrated iron oxide, the color of ocher varies from light yellow to orange-red. Like red iron oxides (), they are found around the world and have been used as pigments since prehistory. French ocher, historically one of the best grades of ocher, contains about 20% iron oxide and is high in silica.
Ocher grades into sienna, a yellow-brown pigment containing a higher percentage of iron ore than ocher as well as some manganese dioxide. Sienna grades into umber, which is darker brown and contains a higher percentage of manganese dioxide. Burnt sienna is brown or bright red, burnt umber is a darker brown than umber.
Ocher is not naturally usable as a pigment and therefore needs to undergo several important processes, such as:
- Extract ore from the quarries.
- Separate ocher from sand using water and centripetal force.
- Blend different ocher extracted from diverse veins to obtain the selected colors.
- Grind to 50 microns and pack.
Permanence and Compatibility
Ocher is among the most permanent colors among the artist's palette. It is compatible with all other pigments, and can be used with good results in all mediums.
Oil Absorption and Grinding
Ocher absorbs a moderately high amount of oil. The oil absorption ratio is 35–45 parts by weight of linseed oil to 100 parts by weight of pigment. If the measurement were grams, umber would require 35-45 grams of linseed oil to grind 100 grams of pigment to form a stiff paste. It somewhat slows the drying of oil paint, but forms an excellent film.
Ocher is not considered toxic, but care should be used in handling the dry powder pigment to avoid inhaling the dust.
Pigment: Italian Dark Ocher
|Colour Index:||Pigment Yellow 43 (77492)|
|Chemical Name:||Iron Oxide Hydroxide|
|ASTM Lightfastness Rating|