Making Raw and Burnt Umber — The Manganese Earth Pigments of Warm Shadow and Deep Brown

Obtain raw umber earth from a geological supplier or art pigment dealer. Quality umber is a dark, cool brown with a distinctly greenish undertone when spread thin — this greenish cast is the hallmark of high manganese content. Rub a sample across white paper or an unglazed tile: the streak should be a cool grey-brown, not a warm reddish-brown (which would indicate low manganese, closer to a dark ochre). Cyprus umber is traditionally considered the finest quality. Remove any stones, roots, or organic debris.

Break the raw umber lumps into small fragments using a stone mortar and pestle. Pound and grind until the umber is a coarse, gritty powder with no pieces larger than a grain of rice. Wear a dust mask — umber dust is non-toxic but mineral dust should not be inhaled. Umber is typically softer and easier to crush than ochre because of its higher clay content, so this step goes quickly.

Place the crushed umber in a large glass settling jar and add water at approximately 5:1 ratio. Stir vigorously, then let stand for 30 seconds — the heavy sand and grit will settle immediately. Pour the cloudy brown suspension through muslin cloth into a second settling jar, discarding the coarse sediment. Let the second jar settle undisturbed for 4-6 hours, then carefully pour off the clear water above the settled pigment. Repeat if needed. The levigated raw umber should feel silky-smooth between the fingers with no grit.

Spread the wet pigment paste on a clean glass surface and let it dry completely (1-2 days). Once dry, break the cake into pieces and grind half on a glass muller to a fine, smooth powder. This is your finished raw umber pigment — a cool, dark greenish-brown. Store in a sealed glass jar. Reserve the other half (as dried cake or coarse powder) for calcination in the next step.

Place the reserved raw umber in a clay crucible or refractory dish and heat in a kiln or over a strong fire. Bring the temperature gradually to 300-500°C and hold for 30-60 minutes. Watch the colour change: as the goethite converts to hematite and the manganese dioxide partially oxidises, the cool greenish-brown shifts to a rich, warm reddish-dark brown. The exact temperature determines the final shade — lower temperatures produce a more moderate warming, higher temperatures a deeper, more reddish tone. Do not exceed 600°C or the pigment may lose chroma and become dull. Let the crucible cool completely before handling.

Once cooled, grind the calcined umber on a glass muller to a fine, smooth powder. Burnt umber should feel silky and produce a warm, rich reddish-brown when rubbed between the fingers. Compare it side by side with the raw umber from step 4 — the difference is dramatic: raw umber is cool and greenish, burnt umber is warm and reddish. Store in a sealed glass jar. Both pigments are permanent, completely lightfast, non-toxic, and compatible with all painting media. Burnt umber is especially valued in oil painting as an underpainting colour and for glazing warm shadows — the manganese content means it dries faster than any other earth pigment in oil.