Understanding Ochre – World’s Oldest Known Natural Pigment

The term Ochre has been derived from the Greek word ‘Ochros’, which translates in English to ‘Yellowish’. Interestingly naturally occurring Ochre are red in color and not yellow. However, a mixture of other components or other geological processes results in the color variation of Ochre.

The Ochre pigments are fundamentally made of iron oxyhydroxide. It means they contain various proportions of Iron (Fe3 or Fe2), Hydrogen (H) and Oxygen (O). The variation in proportion and presence of other components decide the color of the Ochre. For example, extra manganese oxide can result in browner color. Generally, the Ochre is named after its color and the place from where it is extracted. Some prominent examples are Naples Yellow and Spanish Red.

Diverse shades of Ochre have been seen in prehistoric cave paintings as old as 350,000 years. One of the earliest certain pieces of evidence of the use of Ocre was about 285,000 years ago in the Paleolithic period. Archaeologists have discovered 70 pieces of Ochre weighing about 5 kilograms from a Homo Erectus site in Kenya.

Archaeologists have also excavated small concentrates of Ochre from an early Neanderthal site in the Netherlands dating back 250,000 years ago. They discovered that early humans had figured out a way of using Ochre by mixing it with water to paint their skin or clothing in color. One of the earliest dated painting kits was discovered in South Africa, dating back 100,000 years ago. The kit was a shell which contained finely grounded Ochre and charcoal.

The use of Ochre for cave paintings began 75,000 years back and has been found in several old sites across continents and cultures. Interestingly Ochre was also used for burials. The renaissance period accelerated the use of Ochre as a color pigment. Artists across Europe extensively used Ochre in their paintings. The ease of use, high availability and the dark red color it produced were some of the reasons it was quickly accepted. By the 18th century, Ochre mining and its industrial processing had started. Over the last two centuries, these processes have evolved rapidly. However, today the use of Ochre is slowly getting replaced through synthetic color production.

The mining process of Ochre was not significantly different from other minerals. Starting from small excavations to underground and open shaft mining, Ochre has seen a similar evolution in the mining process. The major difference, if any, was in how the mining product was handled, as Ochre is softer than its other clay counterparts.

Initially, Ochre was crushed or ground into fine powder. It was then mixed with various elements like water, oil or juice to convert into a paste. This paste was then rolled into balls just like clay for trading. Many small mining operations follow this method today, but most large-scale mining operations convert Ochre into fine powder. This powder also goes through a lot of post-processing to ensure a high-quality end product.

In the modern day, the term Ochre is used for a family of earth color pigments. However, the prominent ingredient of these pigments continues to be Ferric Hydroxide or limonite. Following are the different major types of Ochre:

• Yellow Ochre: FeO(OH)·nH2O – The most common hydrated iron hydroxide, also called gold ochre, depends on the intensity of the yellow color.
• Red Ochre: Fe2O3 – The naturally occurring state of Ochre, its red color intensity, varies depending on the mineral hematite’s presence.
• Purple Ochre: Chemically, it is the same as the Red Ochre, but the particle size results in deviation in light diffraction properties resulting in a different hue.
• Brown Ochre: FeO(OH) – A partly hydrated Ochre, it is also called Goethite, and its brown color is dominant.
• Sienna: This Ochre type contains limonite and a small proportion of manganese oxide, which results in a darker shade than natural Ochre.

Apart from the variations mentioned above, there are still many other naturally occurring color pigments. For example, Umber pigments contain a larger amount of manganese, almost up to 20%, which makes the color dark brown.

One of the essential properties of Ochres is that they are non-toxic. Hence they can be used to make oil paints that can be used without any challenges. Oil paints made out of Ochre have the property of drying quickly and thoroughly covering the surface. That is why oil or other liquid agents are often used with them.

Unlike other clay extracts, Ochre have a lower heating point and is not chemically inter. In acids, they would dissolve quickly, leaving behind a yellow solution. When heated, most of the Ochres turn red as they start to lose their hydration. Various degrees of heat are applied to Ochres and mixed with other components to create shades of color ranging from white. The color pigments are generally insoluble in water and are used as grounded fine particles mixed with liquid agents.

While Ochre mining is not very challenging given the soft nature of the extract, what is more, important is the processing that the extract goes through. Therefore, JLD Minerals have streamlined its processing processes using the latest state-of-art technology and a highly skilled workforce. This ensures that the extract is converted into the purest product and customized to the client’s needs.