Whitstable Castle

In the 15th century there was a real need for ‘alum’ a mineral used mainly for fixing dyes in cloth so that colours did not run. Queen Elizabeth I gave a licence to search for deposits and a new site was found in the cliffs at Tankerton. The resulting product was called “Copperas”. The first mine opened in 1588 and for 200 years the owners made a great deal of money from what effectively was one of the world’s first chemical industries. A Copperas House was built on the site that is now the almshouse. Others smelting works were built where the bowling green is, by the Harbour and on the site of the Castle Tea Gardens, located on Tower Hill.

Workers wore small metal masks which gave little protection from the terrible fumes. The pyrites were collected by the poor, left to decompose and processed by heating and cooling in huge vats. The resulting green vitriol crystallised to form copperas. A report in the “Kentish Gazette” of February 1788, describes how a worker slipped into a vat and died 26 hours later. The harbour grew as trade expand.