The Chemistry Behind Stone Age Art

In the Stone Age, chemistry was unknown. However, humans had learned the use of pigments for making pictures and symbols. We can see them in caves around the world. How did they know about these pigments?

Cave Art around the world
The next time you take a vacation, we suggest you visit Bhimbetka. Deep inside Madhya Pradesh, this place has many caves where humans have made many beautiful paintings. Did you know that these paintings are as much as 30,000 years old?

There are caves like Bhimbetka in other parts of the world too. The caves of Lascaux in France are world famous, but tourists are no longer allowed there. Blombos in South Africa, Nyero in Uganda, Mulege in Mexico and Kakadu in Australia are other famous sites, where Stone Age paintings can be seen on the walls of caves.

What made them last so long?
Paintings made with oil or watercolour can fade after a few decades. So what made these rock paintings last?

Most of the painted caves are found either in deserts or deep underground. The air in these caves became very dry over time, and no bacteria or fungi could grow. If they could have grown, they would have released carbon dioxide, which would dissolve in moisture to form carbonic acid. Over time, the carbonic acid would corrode the paintings. In caves that weren’t dry enough, the paintings were not so lucky over, vanishing over time. Examples of this are the cave paintings of the Ajanta Caves, which are located in a dense rain-forest. Even though they are just a few hundred years old, only a few fragments remain, on walls that were once richly painted over.

How were these paintings made?
In those days, sophisticated oil paints or water colours were unknown. However, many Stone Age tribes knew the use of coloured mineral pigments. Today we know that these pigments are made of minerals like barium manganate (blue), haematite (red), gypsum (orange), malachite green or limonite (yellow). These are all oxides. Oxides of iron, known as ochres, were also used to make yellow, red or brown colours.

These minerals are sometimes found in caves (which is why Stone Age art is found only in some caves). To make a pigment, the mineral was crushed into gravel by pounding with a big stone. The gravel was then ground between stones to make a powder. The pigment was then mixed with wet clay, gypsum or lime to make a paste that was ready to paint.

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