Copperas is a green iron sulphate chemical that is used in the dyeing process. Copperas production was undertaken at Queenborough from at least 1579 when Mathias Falconer was operating probably the first works for the manufacture of this dyestuff in Britain. The works was probably located at this site and a description of 1634 speaks of a 1 acre site being used to process pyrites brought from Essex. The copperas beds were in the northern half of the site while the processing buildings, boiler house, warehousing etc was clustered against the wharfs at the south end of the site. In 1886 Hall's works closed and the site was taken over by the Stevens Chemical Manure Co. who had been manufacturing superphosphates from bone at a plant in London since 1847. The new works was named the Sheppey Glue and Chemical Works and by 1900 was using a three chamber absorption plant to create sulphuric acid for use with bones in the production of superphosphate fertilizers. The works also made compounds and potash salts from kelp and glue from bones. The site has subsequently been redeveloped