Pigment History
The Gargas Quarry provides Dark Yellow Ochre
The Rustrel Quarry provides Light Yellow Ochre.
Société des Ocres de France main office in Apt.
Known since antiquity, ocher (Okhra in Greek, meaning yellow soil) occurs naturally as yellow ocher (the iron oxide limonite) or as red ocher (the iron oxide hematite).
Use of color may have taken place half a million years ago and involved body painting. Within the last hundred years Prehistoric people, Neanderthal and Cro-Magnon, used red ocher in burial and fertility rites, possibly as a symbolic replacement for blood. The most dramatic use of ocher was in the cave painting found in France (Lascaux and Chauvet), Spain and North Africa. They used basic colors such as: red and yellow ocher, sienna, black (charcoal & burnt wood) and white from burned bones or kaolin. Other natural colors were discovered later by other civilizations such as Egypt, Greece and Rome.
The history started 110 millions years ago when Provence was covered by sea which deposited a mix of grey clay and sea sand full of mineral, such as Glauconite the faraway ancestor of Goethite which colors ocher from yellow to orange.
Ochre history is complex. It is made of two phases which followed one another during geological periods. First of all, it is necessary to imagine that during the cretaceous era (the lower cretaceous to be precise) the region was covered by a shallow "epicontinental sea". At the bottom of this sea, materials from the close continent, primarily quartz grains, piled up and thus settled sand masses. These sediments were rich in underwater animal life traces: remains of all kinds of shells, many lamellibranches: oysters, mussels, etc…, of sea urchins and especially of Foraminifera, very small organism, which residues can be detected in the thin slides studied with the polarizing microscope. After the sedimentation phase, with the contact of sea water, a green mineral was formed on the seabed: the glauconie. This mineral (variety of clay) has the characteristic of containing, in its crystal lattice, iron atoms. This crystallochemical characteristic played a very important part in the continuation of the ochre history.
During the higher cretaceous appeared the second phase, which leads to the creation of ochre. Due to the tectonic movements, the lower cretaceous marine deposits were raised and emerged. A new continent was born. This continent underwent immediate severe climatic conditions. At this time, Provence was in a tropical equatorial type climatic context (our area was close to the equator). This climate originated intense "lateritic" deteriorations, which led to the dissolution of the majority of minerals from the original marine rocks, such as the glauconite. This one, while dissolving by hydrolysis, released in the weathering medium its iron atoms. Thus the goethite materialized. As of its individualization, the rocks of the new continent were naturally colored. Ochre had just been born. At the same time, weathering had shaped kaolinite crystals, because this pure aluminosilicate remains the only stable argillaceous mineral under such conditions of tropical weathering. The various facies created by the paleo-weathering are not randomly spread: they are managed according to a precise vertical continuation, which composes a "lateritic weathering profile". At the base profile, are the green rocks, which are the glauconitic "mothers" marine rocks. Above, are superimposed the various colored facies of the ochre sands, themselves surmounted by the facies of the tropical grounds: kaolinic siliceous white sands (which are the old ochre sands secondarily "bleached" by scrubbing of iron oxides) and, at the top of the profile, the shells: white quartzic sill (siliceous shells) topped by the traditional brown ferruginous shell (here primarily goethitic).
Thereafter, the climate having changed, the Cretaceous rocks were covered by other deposits, of tertiary age, initially continental (Eocene) then again marine (Miocene). And it is only by means of great quaternary scorings that the Cretaceous rocks arrived at the outcrop such as one can observe them nowadays. Observations amplified at the level of ochre cliffs, artificially created at the time of the last centuries mining.
Mineralogy
Even if Greek word OKHRA means only yellow ground, Vaucluse ochre offers an infinite pallet of hues, turning from the pale yellow to the sharp red and by multiple orange. These colors are due to a mineral pigment: an iron hydroxide, called GOETHITE. In the red ocher, obtained by heating in a furnace, the glowing pigment is iron oxide: the HEMATHITE. In natural ochre, the crystals of goethite are associated with a clay: KAOLINITE. And it is the intimate association of these two minerals which truly constitutes the "ochre" pigment.
The rock itself is a sandy formation, made of quartz grains "cemented" by an ochre coating. The crystals which form ochre are of very small size: kaolinite and goethite crystallites measure more or less a micron, so one can observe them only under the electronic microscope. Mineralogical composition of the ochre material, extracted by cleaning the sands:
- Kaolinite, which is the essential argillaceous support
- Goethite, which is the colored pigment
- Quartz, never absent (even in the finest washed and sorted fractions)