EXTRACTION
Ochre is extracted from ore. It is found in fairly even horizontal layers of variable thicknesses, some of which can be as high as 35 meters.

The ore in these layers is quite dense and it has to be broken up with a bulldozer. The ore is composed of between 80% and 90% of very fine siliceous sand and between 10% and 20% of ochre.

If the now-disused galleries of Gargas were laid end to end, they would stretch for 40 kilometres, two thirds of the ore in these galleries having remained in place in the shape of pillars, to ensure that the structure remained stable. It is remarkable that, thanks to the density of the ore, the galleries – which at times reach 7 metres in height- were formed without the need for any reinforcement. They are like underground gothic cathedrals!

Wherever there is a non-ochreous layer no thicker than the seam of ochre below it, it is removed by open-mining techniques. The top layer is bulldozed away and kept, so that later it can be used to rebuild the site. Then the ore is removed by bulldozer. Terraces five metres wide are left to keep the whole structure stable and to reduce the risk of falling rocks. The evacuation of the ore is done by trucks which transfer it onto the wash down.

Until 1960, the sand was removed by a process known as ‘levigation'. This meant that a jet of water was directed onto the ore in a coffer-dam (a special basin). The heavier sand sank to the bottom, whilst the ocre floated in the water above. This ore-bearing water flowed over into ‘drying tanks' 200 square metres in size. This process was repeated every day, until the tanks were full, with the wind and the sun drying out the ochre. Through this process, 200 kilos of ochre were produced from every cubic metre of ore.

Starting in May, when the ochre had taken on a firm consistency,blocks of ochre were used to build up ‘walls' around the tanks and these were then left to dry out further in the sun and wind.

Today a different method is used. There are no more coffer-dams. Instead the ore and sand mixture is pumped at enormous pressure into a container where, because of the centripetal pressure of 500 grams per square centimetre, the sand is forced into the centre of the drum and leaves the ochre-bearing water to flow out into channels leading to the ‘drying tanks'. The pump and the drum are both lined with rubber to protect them from abrasion by the sand.

 DECANTATION
The last stage of the washing of the ochre is called ‘decantation'.

The ‘drying tanks' are filled with water and the heavier ochre settles at the bottom of the tank. Applying the same system as in wine-making (where the top layer of liquid passes out of the container through a special ‘stopper') the water is drawn off. After that, each drying tank then has a layer of about 50 centimetres (approximately 60 tons) and the summertime drying period (May to September) starts.

The iron oxide of untreated ochre is a hydrated oxide. If one bakes ochre at a temperature of between 800 and 900 degrees, it is changed into a ferric oxide ore. The yellow colour changes to red.

The ochre used to be baked in wood ovens, but these days it is done in fan-assisted gas ovens. These ovens, 15 metres long and 1 metre in diameter, are covered in bricks to conserve the temperature more effectively. After a few days of cooling, it is ready to be pulverized and packed into bags.

To obtain the required colours, it is necessary to mix different ochres produced from different ores. The mixture is then placed in a grinder where the ochre is pulverized to 50 microns Finally it is packaged into 25 kg. paper bags.

Ochre is put to many different uses. It is used in the building industry for colouring renders, whitewashes and distempers, concrete, etc. It is used in painting, both for decorating buildings and in art. In agriculture it is used to colour fertilizers. It is also invaluable in pottery and ceramics, for colouring tiles, in cosmetics (to tint face powders and blushers, for example). The residues from ochre production – the coloured sands – are also used by the national electricity and telephone companies for filling in trenches. Ochre from Provence travels the world! 60% of the ochre produced by us is expored to other parts of Europe, the USA, Africa, the Middle East, etc...