Our Luberon Red Ocher is from ocher deposits in the French quarries of Gargas and Rustrel nestled in a 12 mile long enclave in the heart of the Luberon Massif, the ocher country. Ocher is a symphony of colors ranging from pale yellow through the orange range to an intense red. It has two major characteristics: it does not fade in daylight and the color is highly concentrated.
Rublev Colours Aqueous Pigment Dispersions are pigments dispersed in water ready to be mixed with water-based mediums. These dispersions are especially made for use with traditional painting mediums, such as egg, casein, fresco, watercolors and distemper (glue tempera). They are also ideally suited for use with gesso for making toned grounds for drawing and painting.
Pigment dispersions from Rublev Colours contain only naturally-derived ingredients, in addition to pigment and water, making them ideally suited for traditional and natural mediums. Unlike other pigment dispersions that are typically made for acrylic medium, Rublev Colours Aqueous Dispersions do not contain coalescent solvents, artificial dispersing resins and other additives that interfere with natural mediums.
Rublev Colours Aqueous Dispersions make preparing traditional mediums easy; you do not have to hassle with powders, grinding pigments with expensive tools and calculating pigment-binder ratios to make water-based paint. They make adding the right amount of paint binder simple and easy. For example, preparing egg tempera has never been easier, because the dispersion makes measuring the right amount of pigment easy—you simply add egg and stir—there's no guessing how much egg to add to the pigment.
Origin and History
Known since the antiquity, ocher (okhra in Greek) occurs naturally as yellow ocher (goethite) or as red ocher (hematite). Ocher has been used as a pigment since prehistoric times and is perhaps the most widely used pigment for artists paints.
Red ocher is a natural earth containing clay tinted by iron oxide and is composed of the mineral goethite with clay and quartz, and traces of accessory minerals, such chalk, gypsum and manganese carbonate. Luberon red ocher is made by calcining yellow ocher at high temperatures for a brief period. Historically, yellow 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 goethite, akaganeite and lepidocrocite. The names for yellow 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 (hematite), 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.
Yellow 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.
Direct from the earth, 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.
- Calcine (roast) raw yellow ocher to obtain red ocher by heating it for 15 minutes at a temperature between 500° and 600° C. (932° and 1112° F.).
- Blend different ocher extracted from diverse veins to obtain the selected colors.
- Grind to 50 microns and pack.
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
Red ocher absorbs a low to moderate amount of oil. The oil absorption ratio is 20–25 parts by weight of linseed oil to 100 parts by weight of pigment. If the measurement were grams, it would require 20-25 grams of linseed oil to grind 100 grams of pigment to form a stiff paste. It forms an average drying oil paint, and makes a good paint film.
Ocher is not considered toxic, but care should be used in handling the pigment to avoid ingestion.
Aqueous Pigment Dispersion: Luberon Red Ocher