In 1980,an experiment tested how long various pigments and binders would last.Twenty-three years later some of the paints had disappeared, but others were still fresh. For colour, the pigments used were red and yellow ochre and specularite. The binders were blood (with and without serum and fibrin), fat (beef and ostrich) and water. The mixtures were painted onto blocks of quartzitic sandstone. They were left outside on a shelf where they were sheltered from the rain and sun, except for late afternoon winter sun.