Percival Norton Johnson
Having trained in his father's business as an assayer, Percival Johnson established his own firm in 1817. He specialised in the assaying and refining of precious metals particularly gold imported from Brazil: he perfected a method of extracting the Palladium from the gold therefore improving the gold's colour. He became a Fellow of the Royal Society in 1846. He went into full partnership with George Matthey, a stockbroker, in 1851. His expertise in refining earned his business the appointment of Assayer to the Bank of England in 1852.
- Cottington, Ian E. (23 September 2004). "Johnson, Percival Norton". Oxford Dictionary of National Biography. Retrieved 29 November 2021.
- Stabb, J. (17 October 2020). "Stoke Fleming, Some Old Devon Churches". GENUKI UK & Ireland Genealogy. London: Simpkin et al (1908-16). p. 221. Retrieved 29 November 2021.
- Biography of Percival Norton Johnson, published by Johnson Matthey, 1951