Could hematitic paint save the world? The climate-saving potential of hematite films.

I do earth pigment rock art because I think we need to change our relationship to the planet. We need to feel less disconnected from it, and what better way to achieve that than through a “right brain” artisitc, creative engagement with clays and rocks to make earthy paintings of natural fauna on piece of rock? It’s a time-out, a break from the rat race of progress in the technological age, a return to an earlier time, a step away from the need for development and progress. I feel myself becoming once again a member of that ancient stone age clan: the People of Ochre.

A Most Inclusive Clan

All the same, I like to be a bit paradoxical, so I’m not a total luddite, and in fact I find it interesting to ponder how that favourite Earth pigment – hematite rich red ochre – is part of a long human story of technological development. It turns out that the People of Ochre clan is so inclusive that it encompasses rather than excludes the Neolithic and Classical cultures.

Hematite and human civilisation go hand in hand. Humans have had a great interest in hematite for a very long time. Indeed, there is evidence that we first started using it for decorative purposes as long as 100,000 years ago. Haematite, with its iron oxide content, is the mineral that gives red ochre and orange clay their colour. Its use in rock art as a potent paint with a long lasting stain on silicate-containing rocks spread around the world with the exodus of the first anatomically modern humans out of Africa (if not before). It was probably very early on that we discovered that heating yellow chore (containing hydrated iron oxide) would turn it, as if by magic, into red ochre – the first chemistry experiment?

Left: Red ochre bison, Altamira, Spain; Right: Roman mosaic, Verulamium, with terracotta tesserae

Pottery, roofing and Iron

The use of pottery was a major cultural shift, and as we started making clay pots, we continued using hematite-containing clays, also baking them to make roof tiles, so that the iron-oxide look continued to be a major feature of the aesthetic of towns in the classical world. We also made bricks from clay, and came to prize red-figure vases using red clay slips and terracotta amphorae as objects of beauty, as well as continuing to use ochre-based paints a great deal. Even as we left the stone age, the association continued: hematite is one of the principle iron ores from which we learnt to smelt iron, heating it at high temperatures along with charcoal, so the carbon combined with oxygen to make carbon monoxide, which reduced the iron oxide in the hematite, leaving pure iron and slag.

Hematite and Cheap, Clean Energy

And this close relationship between human culture and hematite may be set to continue. What the world needs now is dirt cheap clean power. A great number of geopolitical tensions and conflicts would evaporate and climate change could be far more effectively mitigated if energy was clean, easy and cheap as chips, and a shift to green transport and heating would be a synch if it was cheap. Hydrogen is a clean fuel – whether used in a combustion engine or a fuel cell. A fuel cell’s only waste product is water. But how do you get the hydrogen, cheaply?

Hydrogen can be obtained by water splitting – splitting apart the hydrogen and the carbon. This can actually be achieved using concentrated sunlight, with iron oxide (such as hematite) being placed in the water as a photocatalyst. It’s something to do with electrons and electron holes. (Don’t press me for the details.) This is very promising because hematite is cheap, and so is water, and sunlight is free. OK, you need a bit of apparatus too, but nothing too pricey.  With plain hematite, it’s an inefficient process, but progress has recently been made using things like mesocrystals of hematite that have been ‘doped’ with metal ions. And even undoped nano-films are proving promising. And it looks like this can still be done without adding too much extra cost.

Coating objects with films of haematite is the root of human culture; it’s what rock artists did for thousands of years. Wouldn’t it be funny if it turns out this is the way forward for human culture too?