Produced by Humphry Bowen

Humphry Bowen

Humphry John Moule Bowen was a British botanist and chemist.Bowen was born in Oxford, son of the chemist Edmund Bowen. He attended the Dragon School, gaining a scholarship to Rugby School and then a demyship to Magdalen College, Oxford...

, the reference material called Bowen's Kale was used for the calibration

Calibration

Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device....

 of early scientific instruments

Measuring instrument

In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...

 intended to measure trace elements in the 1960s. With Peter Cawse, Bowen grew, dried and crushed a large amount of kale

Kale

Kale is very high in beta carotene, vitamin K, vitamin C, lutein, zeaxanthin, and reasonably rich in calcium. Kale, as with broccoli and other brassicas, contains sulforaphane , a chemical with potent anti-cancer properties. Boiling decreases the level of sulforaphane; however, steaming,...

 (Brassica oleracea) into 100 kg 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

Standardization

Standardization is the process of developing and implementing technical standards.The goals of standardization can be to help with independence of single suppliers , compatibility, interoperability, safety, repeatability, or quality....

. It stimulated preparation of further materials by other organizations for similar use.