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 preparation of further materials by other organizations for similar use.