Ochre, it turns out, is not just one substance. It is any of a variety of natural earth pigments that consist of ferric (iron) oxide, clay and sand and it ranges in color from red to yellow, to green, blue and purple; that is, it pretty much covers the spectrum of the colors the human eye can see. In keeping with the third lesson, here’s a definition of ochre from the Encyclopedia Britannica: “a native earth coloured with hydrated iron oxide. It varies in colour from pale yellow to deep red, brown, and violet. There are two kinds: one has a clayey basis, while the other is a chalky earth.”

Ochre was probably the first substance used as paint. Materials found in the Middle Paleolithic levels of Blombos Cave in Cape Town, South Africa, are presumed to be a “paint kit,” consisting of an abalone shell and a stone, probably used to grind ochre and bones together and to mix the powder with a liquid or fat as a binder. Habitation of this cave by mid-Stone Age people dates to about 75,000 years ago. A stone flake from Blombas bears cross-hatchings made by red ochre, possibly a red ochre crayon; it is the first drawing by Homo sapiens of which we know. The cave was nominated as a UNESCO World Heritage Site in 2019.

During the Middle Ages and the Renaissance some of the best ochre was mined in Italy and France and that remains true today. The modern colors sienna and Venetian red, for example, reflect that history. Paintings by Vermeer and Rembrandt exemplify the widespread use of ochres in early oil painting. Before (and for that matter after) oil paints were invented ochres were used to make tempera paint, which usually uses egg as a binder, and it was applied directly to fresh, wet, lime plaster in frescoes. A chemical reaction as the plaster dries binds the pigment to the plaster.

Many researchers consider the use of red ochre a proxy for the development of human abstract and symbolic thought. (Red represents blood and life, for example, and that’s why it was used in burials, so the thinking goes.) Others warn we may be venturing too far into ethnocentric thought when we assume that the use of red ochre in burials, for example, has symbolic meaning. The pigment, after all, has other, practical, characteristics: It can function as a sunscreen, an insect repellant, an adhesive, a preservative for leather, and a disinfectant.

In an example of bio-mimetic (more new vocab) transfer, people may have learned about some of these properties by observing vultures, a 2016 article in the journal Animals proposes. Humans and turkey vultures competed for the same carcasses. The vultures, after feasting on dead meat, bathed themselves in puddles containing red iron oxide (ochre). Ochre, exposed to sunlight, produces chemicals that can kill viruses and bacteria and convert the inevitable disgusting odors on feathers and skin into CO2. So covering one’s body in red ochre may have had sanitary and esthetic benefits for early hunter-gatherers.

A Spanish paleontologist, Carlos Duarte, has suggested that using red ochre as a pigment in tattoos (or absorbing it in other ways) could have been a factor in the evolution of the human brain. The iron in the pigment could have entered the blood stream and facilitated the transport of more oxygen to the brain, thus accelerating the development of intelligence.

Maybe. But it doesn’t seem to have helped the vultures much.

And none of this helps me find red ochre. (So much for the fourth lesson.) However, yellow ochre, heated (or calcined) to at least 480 degrees Fahrenheit, turns red. And I have found yellow ochre. Stay tuned.