Copperas. An account of the Whitstable works and the first industrial-scale chemical production in England
Tim Allen, Mike Cotterill and Geoffrey Pike
Canterbury, UK: Canterbury Trust Occasional Paper No. 2, Canterbury Archaeological Trust 2004 | Pp64 | 13.95 | ISBN1870545087
Reviewed by Bill Griffith

In 1995 an array of timber posts set in poured yellow mortar was exposed by marine erosion on the foreshore of Tankerton Bay, Whitstable, Kent. The Canterbury Archaeological Trust conducted a two-year investigation of the site and showed it to have been a factory for copperas. This book tells its story.

Copperas is a 15th century term for 'green vitriol', ferrous sulfate (FeSO₄.7H₂O). Although the use of various vitriols goes back to Babylonian times and is mentioned by Pliny, it became important in Europe in medieval times, when in England a search was made for local sources.

A letter by the Lord Treasurer, Sir William Cecil, in 1565 alludes to the material and by the 17th century a number of plants were established in the Thames estuary and around the coast. By the mid-1750s England had become the largest producer in Europe.

The copperas was made from nodules of iron pyrites (marcasite) from the seashore, placed in clay- or chalk-lined beds and left to weather for six years. The 'liquor' thus produced by atmospheric oxidation and hydrolysis consisted of ferrous sulfate in sulfuric acid. This was boiled with scrap iron for 20 days and deposited crystals of copperas. This was used in the textile industry as a mordant for wool and, with oak-gall, as a black dye.

The Tankerton copperas production started in the mid-16th century and continued until 1835, and is claimed to be the earliest industrial-scale chemical factory in England.

The excavation report is followed by a description of the copperas extraction process. The book also emphasises copperas' role in various industries and offers a history of the industry and its complex relationships with those in the Low Countries. Finally the history of the Whitstable works is examined.

The book is well written with colour illustrations and it offers a fascinating glimpse of what was once an important local industry.