I made this wheel using black iron oxide, a couple caput mortuums, a couple red earths, haematite, and several ochres. I added a little bit of beech charcoal to the deep blue on the right and I also mixed in titanium white throughout. All the earth pigments are essentially iron oxides. The medium is acrylic.
You can make a complete color wheel using just iron oxides and white. Iron oxide comes in yellow, orange, red, violet, and black. The black can be lightened into a blue by adding white. That's how I got the blues above. And then you can mix the yellow oxide or the red oxide with the blue to get green or violet. That's how I got the greens above. The violets in the wheel are caput mortuum and black iron, but I could just as easily have made them with black and red.
Here are some iron oxide pigments I formed into round pastels to draw with. You can see the huge range that we can get with iron oxides.
A good project for students is to make a color wheel like the one I made using yellow oxide, red oxide, black oxide (Mars Black) and a white.
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Then they can make a painting using this limited palette. They can use oil, acrylic, water color, or gouache.
I made this painting using just terra rosa, yellow ochre, a mars or ivory black, and titanium white. Four pigments was all I needed.
Some dry earth pigments don't mix well with linseed oil. Since I used acrylic for my wheel, the dry haematite, caput mortuum, and one of the orange ochres worked okay, but these three in particular have trouble getting along with the oil. It doesn't stop me from playing with them, however. I love playing in dirt.
