Bowen's Kale

Produced by Humphry Bowen, the reference material called Bowen's Kale was used for the calibration of early scientific instruments intended to measure trace elements in the 1960s. With Peter Cawse, Bowen grew, dried and crushed a large amount of kale (Brassica oleracea) into 100kg of a homogeneous and stable powder in 1960 that was subsequently freely distributed to researchers around the world for over two decades. This was probably the first successful example of such a de facto standard. It stimulated preparation of further materials by other organizations for similar use.