Paper, an account of the way of making English green copperas by Daniel Colwall Concerns copperas stones or 'gold stones' [pyrite] found on the coast of Essex, Hampshire and further west, from which can be produced copperas [or 'green vitriol', a green, crystalline iron sulphate]. This process is described with reference to the innovative methods used at the copperas works of Sir Nicholas Crisp at Deptford where beds are constructed to produce the 'liquor' or 'vitriol' and siphon it into cisterns to be heated with iron, then cooled, to produce copperas. Read to the Royal Society on 8 May 1661 Subject: Geology / Mineralogy / Industry [1661]