text: 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.
  With Peter Cawse, Bowen grew, dried, and crushed a large amount of marrow-stem kale (Brassica oleracea var. medullosa) into  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. Bowen's Kale stimulated preparation of further materials by other organizations for similar use.