Yellow ochre

/ oak • ur /

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How Yellow ochre is made:

Origin: artificial  

Natural mineral:

Red and yellow ochre pigments abound at the surface in Minas Gerais, Brazil. Pigments like these were readily made into paints by prehistoric peoples (such as the nearby Santana do Riacho, Lago a Santa) who would then paint with their fingers or with vegetable paint brushes.

Yellow ochre from Spain

Artificial variety of pigment Reaction of cobaltous salts with acetic acid and subsequent mixing with concentrated solution of potassium nitrite.
In the lab
Materials needed: Cobalt(II)-chloride (CoCl2 · 6H2O), potassium nitrite (KNO2), acetic acid
Safety (MSDSs): Cobalt(II) chloride, potassium nitrite, acetic acid (at Fisher Scientific)
Method: 1 g of cobalt(II)-chloride is solved in 20 ml of deionized water and acidified with approximately 1 ml concentrated acetic acid. 8 g potassium nitrite is then solved in 20 ml of deionized water and slowly added to the cobalt chloride solution. The resulting precipitate is washed and filtered off.

Illustration of the process:

Picking iron oxide by hand in Hiwassee, Virginia. Mining for pigments is desirable work in Virginia, where the quarry mines are open pits and above ground, and relatively safe.

Mining iron oxide with a mechanized scoop.

The ground pigment:

Pile of ground Yellow ochre