Edward Bancroft (1744-1821), physician, chemist and spy

Edward Bancroft was born in Westfield, Massachusetts, in 1744. He was apprenticed to a physician in Connecticut before going to sea at 18; subsequent to this he settled in Dutch Guiana and practiced medicine. In 1767 he moved to England and studied medicine at St Bartholomew's Hospital in London and appears to have been awarded an MB, since this was given as a qualification when he was elected to the Royal Society in 1773; later he was awarded an MD by Aberdeen University. He became a writer and a member of a freethinking circle centred on Benjamin Franklin and Joseph Priestley.

At the time of the American Revolution Bancroft spied for Franklin and was accused of forming part of a plot to burn Portsmouth Dockyard; he turned King's Evidence and provided information to the British Crown whilst continuing to be paid as a spy by the Revolutionary forces.

Bancroft had begun to research the technology of dyeing and calico printing when he moved to England, and in around 1771 he discovered a yellow colourant in the inner bark of Quercus velutina, the American black oak, which he named quercitron and patented (the patent expired in 1799, leaving him in financially reduced circumstances). Quercitron remained in use in industry for over a century. He wrote various influential works on the subject of dyeing, adopting new French chemical terminology and helping to publicise this in the UK; his main work was The Philosophy of Permanent Colours, published 1794. He died at home in Margate in 1821.