Bowen's Kale

Bowen's Kale was a reference material produced by British chemist Humphry Bowen and used for the calibration of early scientific instruments intended to measure trace elements during the 1960s.

[2] With Peter Cawse, Bowen grew, dried, and crushed a large amount of marrow-stem kale[3] (Brassica oleracea var.

medullosa) into 100 kilograms (220 lb) 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.

[4] Bowen's Kale stimulated the preparation of further materials by other organizations for similar use.