The manufacture of ochre
Ochre... What is it ?
Ochre is a ferrick rock composed of white clay (kaolinite) and iron hydroxide (goethite) or iron oxide (hematite). Goethite gives its yellow colour to ochre while hematite tends on reds. This coloured clay is amalgamated with sand grains (quartz) and ochres are found in the soil in the form of ochre ores composed of more than 90% of quartz.
Like in agriculture, all the steps are followed according to the seasons.
How it's made ?
Step 1 : the extraction
Timing : begining of september
Place : Gargas
The first step is extraction. Ochre is extracted from ochre ore. It is in fairly regular layers of varying thickness, some of which can reach 35 metres in height.
In the deposits, the ore is quite compact, which requires the use of a mechanical shovel for winning.The ore consists of 80 to 90% very fine siliceous sands and 10 to 20% pure ochre.
Whenever the sterile layer on the ochre ore does not exceed the thickness of the ore layer, we extract in open air. First, the earth covering the ore is removed with a mechanical shovel. This earth will be set aside for future quarry rehabilitation under the direction of the Department of the Environment.
The ore is then felled with the same machine. Benches of five meters wide and fifteen meters high are made to ensure the facing and to prevent the fall of stones. s.
The ore is removed by trucks and transported to the wash area.
Step 2 : the washing
Timing : spring
Place : Gargas
Until 1960, the disposal of the sands was done by levitation : a current carried the ore in a "cofferdam". The sand, heavier, settled at the bottom. The remaining ochre suspended in the water was carried by the water into settling ponds of 200 m3. The process was repeated daily until the ponds were full. The output of this process was 200 kg per m3 of ore.
As early as May, when ochre had taken on a firm consistency, walls made of ochre clods were built around basins, allowing complete drying under the action of the mistral and the sun.
Today, this method of washing has changed. The "cofferdams" have been removed. The ore with water is sent to a thickening separator (rubber-coated cyclone to prevent abrasion) by a rubber-protected pump to the entrance of the cyclone. The mixture arrives with a pressure of 500 grams/cm2. Under the action of the centripetal force, the sand concentrated on the centre of the cyclone falls, almost dry, and the ochre goes in overflow and is then directed towards the pipe going to the settling bassins.
Step 3 : the settling
Time : spring
Place : Gargas
The final phase of ochre washing is settling. The basins are filled with water and ochre which, heavier, settles at the bottom of the pond. By means of a "drain" system, the water is drained. When the basin reaches a thickness of about 50 cm or 60 tonnes per basin, the drying period from July to the end of August can begin. The ochre is then taken out of the basins and dried, thanks to the help of the mistral, on a large platform.
After that, the ochre will be transported to the factory for the completion of its manufacture.
Step 4 : the calcination
Timing : in accordance with commands
Place : Apt
Iron oxide from raw ochres is a hydrated oxide (goethite). By heating ochre from 800 to 900 degrees, iron oxide dehydrates and turns into hematite. The color, usually yellow, becomes red.
Calcination of yellow ochres or insufficiently red naturally, was made in time by wood-burning oven. Now, it is done in rotary furnaces, heated with gas. These furnaces have a length of 15 meters and a diameter of 1 meter. They are bricked to keep the heat.
The ochre is sent to the head of the oven and received, on the burner side. It takes 15 minutes to cross it. It is, at this moment, baked to perfection. After a few days of cooling, it is ready to be grinded and bagged.
Step 5 : Grinding and packaging
Timing : throughout the year
Place : Apt
To obtain the desired shades, you must mix different ochres or earth. Then, the whole is sent in a pendulum grinder where the ochre is grinded at 50 μ. The packaging is then done in paper bags of 20 or 25 kilos according to the references.
For several years, new packaging has enriched the range.
Okay... But what that's for ?
Today, between 800 and 1,000 tons of ochre are extracted per year.
Ochre is used in many applications :
- In the building industry : for colouring coatings, lime paints, concrete...
- In industrial or artistic paintings.
- In agriculture : for coloring fertilizers.
- For the coloring of terracotta, tiles.
- For cosmetics to colorate powders and eyeshadows.
- In the ceramic industry.
In short, ochre can color any binder !
This ochre is send all over the world : Europe, Africa, USA, Canada, Japan, Australia, New-Zeland, etc and now China.
The ochre residues (coloured sands) are also used by the EDF (french electricity) and Telecom services for the covering of cables in trenches.
At the peak of production, 40,000 tons of ochre were extracted per year in the Apt area. This high production lasted from the 1880s to the 1940s, golden years of the Apt area's production. In addition to the above mentioned uses, ochre was used in the manufacture of rubber in order to thicken it (example : bottle teats, jars rings, bicycle tubes). Ochre was also used in the manufacture of linoleum.
When ochre ceased to be used in the rubber industry, factories began to close one by one in the 1950s (for more information, you can read "The history of our company"). That is for this reason that nowadays, Ocres de France is the last autonomous company in Europe that exploits and transforms ochre ore into pure ochre.
Where do we find ochre ?
Ochre is a pigment used since prehistory. You have surely heard of these magnificent old quarries (the Colorado Provençal, the Sentier des Ocres de Roussillon...) that are no longer exploited since the 1950s but attract thousands of tourists every year. Ochre is found on the five continents but today, the only ochre quarry in activity in Europe belongs to Société des Ocres de France, in Gargas. The factory is located in Apt.
There is another deposit, in Bourgogne, whose proportions are different : the ochre ore is composed of 20% sand and 80% ochre. This quarry is exploited for its clay, but the "discovery" is ochre.
Does an industry necessarily pollute ? No !
The issue of a licence to open an ochre quarry is subject to a public inquiry and an impact assessment.
The extraction authorization is valid for 15 years and the volume is limited (12,500 m3 for the SOF quarry).
Rehabilitation of the quarry is mandatory at the close of the extraction authorization. In 2010, SOF applied to renewal its licence which has been accepted for the next 30 years, thanks to its good conduct and respect of the environment
The quarry and the factory are regularly inspected by the APAV because, like all quarries and factories, they are classified ICPE (french Classified Facility for Environmental Protection).
In Gargas, the Société des Ocres de France has a major advantage : it uses, in closed circuit, more than 300 m3 of water per day to wash its ochre. Only 70 m3 are lost by infiltration. The wash water is pumped into old ochre galleries and returned to these galleries after washing. There is no pollution of water by ochre.
With regard to air pollution, a dust control device is installed on the plant chimneys to purify the fumes resulting from the burning of red ochres and dust control measures are taken regularly.
The rainwater is collected in a large basin to avoid that, charged with ochre, it runs off and pours into the Coulon (river).
The packaging is recycled and office paper is crushed and reused. The particles in the packages are biodegradable. Plastic packaging is made of P.E.T (recyclable), bags in kraft paper and boxes with pallet wood. Finally, all the ochres produced were subjected to a complete analysis in search of heavy metals and nanoparticles.
- A human team, responsive and attentive to customer needs
- Availability of commercial service
- After-sales service & rigorous tracking of the delivery of your parcels
- Close collaboration with suppliers, preferred among local manufacturers
- Strict control of raw materials
- Implementation of environmental recommendations.