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Cover of British Archaeology issue 66

Issue 66

August 2002



Native village that dabbled in Roman culture

Roman mosaic found inches below ploughsoil

Egyptian seal and a ‘cave of jewels’ at Scottish mansion

The 7,700-year-old woman who ate like a wolf

Rare Iron Age temple excavated near Cambridge

In Brief


When Burial Begins
Paul Pettitt on why humans began burying their dead

Chemical Revolution
Tim Allen traces the origins of the Industrial Revolution

Great Sites
Helena Hamerow on the Anglo-Saxon town of Hamwic


The West Midlands in prehistory and the closure of railways


George Lambrick on the importance of museum collections

Peter Ellis

Regular column


The Welsh Border by Trevor Rowley

Digging up the Past by John Collis

The Historical Archaeology of Britain c 1540–1900 by Richard Newman, David Cranstone & Christine Howard-Davies

Genetics and the Search for Modern Human Origins by John H Relethford and The Seven Daughters of Eve by Bryan Sykes

The Extraordinary Voyage of Pytheas the Greek by Barry Cunliffe

CBA update

favourite finds

Val Turner on a Pictish stone that spooked a gravedigger


ISSN 1357-4442

Editor Simon Denison


The Forgotten Chemical Revolution

New research has revealed that the Industrial Revolution began not with coal and iron, but with chemistry. And in the 16th century, too. Tim Allen reports

In 1995, storms and heavy seas exposed a curious arrangement of timbers set in yellow mortar on the Tankerton foreshore, Whitstable, on the North Kent Coast. They were eventually identified as parts of industrial workings where the chemical, copperas, had been manufactured from the late 16th/early 17th century.

Copperas is a little-known chemical today - even among historians. But excavations at Whitstable in the late 1990s, followed by a couple of years of documentary research, have revealed the immense importance that this forgotten chemical played in Britain's industrial development during the 16th-18th centuries. Indeed, the new research - carried out with Mike Cotterill, an expert in the early chemical industry - demands that we reinterpret the origins of the Industrial Revolution, which are traditionally seen as lying in the coal, iron and steel industries of the north of England. Those northern industries were not, in fact, established until some 200 years after the revolutionary copperas industry was fully operational in the south of the country.

Copperas manufacture was wholly unlike the traditional, small-scale chemical industries of the medieval and early modern period such as brewing and baking. It was heavily capitalised. It required huge investment in plant and materials; and the chemical took four years to produce. Such investment required a financial return, and profits were consequently high.

Copperas itself played a key role in numerous industries at the time - especially textiles. And the copperas industry, with its by-product of sulphuric acid, was a direct ancestor of the modern pharmaceutical, detergent, adhesive and fertiliser industries. Indeed, many modern chemical factories are built on or near old copperas works dating back to the 17th century, such as the GlaxoSmithKline pharmaceutical works at Deptford and the Fisons agricultural chemical plant at Ipswich. Copperas deserves to be better known.

Copperas (ferrous sulphate) has nothing at all to do with copper. It is made from iron pyrites (ferrous disulphide), washed out of the coasts of the Thames estuary by marine erosion in the form of thin twig-like fossils called 'copperas stones'.

Fossils into acid

These knobbly, metallic-looking fossils were turned into a mixture of dilute sulphuric acid and dissolved copperas using a dangerous, complicated and highly noxious industrial process (see panel). The industry developed close to the source of copperas stones at many sites in the Greater Thames estuary, mostly on the North Kent and Essex coasts, with factories built in the late 16th and early 17th centuries at Whitstable, Queenborough and Deptford in Kent, and at Brightlingsea and Walton-on-the-Naze in Essex. Iron pyrites also occurs in Hampshire and Dorset, where copperas works, albeit short-lived, were first established in England.

Copperas was closely linked with the woollen industry because it was mainly used as a textile dye fixative, a dye darkening agent and a black dye. On the Kentish Weald, a Cranbrook clothier's inventory dated 1567 mentions 'a c[wt] of copparasse and 5 li (pounds) of allam, 20s' - while copperas was used to darken dyes, alum was used to brighten them.

Copperas was also used to blacken leather and to make writing ink. The Kentish Gazette reported a fatal accident in a copperas ink works in Whitstable in 1788: 'As John Wellard was assisting in running the copperas ink coolers, he unfortunately slipped in. . . Every assistance was given but in 24 hours a mortification ensued and in two hours after, he expired'.

Metal working required nitric, hydrochloric and sulphuric acid - for example in the etching of printing plates - which were all produced using copperas. A ton of copperas yielded (through heating, melting and distillation) approximately 168 lbs. of sulphuric acid, used increasingly by dyers to make better dyes, and by the mid-17th century England had developed a Europe-wide reputation for this acid.

Tonics and potions

Copperas was used as an eye ointment during the medieval period, to treat scab in sheep, and later (presumably in small quantities) as a laxative. The Royal Navy later used it - ineffectively, of course - to treat scurvy, an illness caused by vitamin deficiency. Copperas eventually became the basis for many patent medicines, especially Glauber's 'Sal Mirabile' - a medicine-cum-tonic which was very popular in the late 18th and early 19th centuries - pointing to the link between copperas and the emergent pharmaceutical industry. Most of the medicinal properties claimed for copperas were presumably fallacious, although ferrous sulphate can still be bought in chemists today as a treatment for anaemia.

Sulphur, along with charcoal and birdlime, was a principal component of 16th century gunpowder, and a method of producing it from copperas stones was discovered in 1570. Previously, most of Europe's sulphur had been mined in Sicily, but the European religious wars of the 16th century reduced England's access to Sicilian exports, bringing an urgent need for England to find a domestic supply. Copperas stones met that need.

A pyramid of stones was built over a wood fuel platform. This was then covered with earth and wet ashes, and burnt to produce sulphur. This discovery probably explains the first gunpowder production at Faversham near the Kentish iron pyrites beds in 1573, and the long-term presence of the gunpowder industry there after better forms of gunpowder were developed and sulphur ceased to be used.

The copperas industry in the south of England prospered mightily and by 1764 England was the principal European producer, exporting over 2,000 tons annually in the 1780s. Eventually, however, the southern industry retracted as technological changes made it redundant. By then, copperas and copperas substitutes were being mined in Humberside and North-East Yorkshire, and these products were easier and cheaper to refine. By 1787, southern copperas was used principally for dyeing and ink making and most production stopped in the early 19th century.

However, on the Isle of Sheppey off the north coast of Kent, Stevens Sons and Company still produced copperas at the Queenborough works in 1882, and in 1886 began manufacturing fertilisers using sulphuric acid produced from local iron pyrites. Copperas and sulphur production are recorded there in state papers as long ago as 1579. As the company, still owned by the Stevens family, continues to produce chemical fertilisers to this day, a continuing, 400-year-old tradition of chemical production can be claimed for this remarkable site.

Trouble with the Pope

During the late 15th and early 16th centuries - before copperas stones were discovered in England - the English wool trade was depressed by papal duties on dyes and fixatives, including copperas. The wool trade was the mainstay of the English economy, but the supply of chemicals it required was controlled from Italy. In 1553, English trade interests were further threatened when the Netherlands' Spanish rulers permitted the export of these chemicals only under licence and in 1555 the Pope declared Antwerp the sole market for them. This stimulated an urgent search for domestic sources of copperas in England.

In 1562, a monopoly was granted to a William Kendall to find suitable ores but he failed. Fortunately for the English Crown, papal power was weakening as the Reformation and nascent nationalism gained strength and in 1565, Elizabeth offered potentially lucrative monopolies to 'certain Dutch Mynerall men'. The earliest records of copperas and sulphur production at Queenborough on the Isle of Sheppey, in 1579, state that they were in the hands of a 'Brabander' or Dutchman named Mathias Falconer.

Early interest in the Whitstable copperas industry is recorded in a letter written in 1569 by the Archbishop of Canterbury to Sir William Cecil. Referring to an unidentified 'poor man', the archbishop wrote: 'This poor man . . . signifieth that by the councel of a stranger he hath found out the making of brimstone (sulphur) on the shore of Whitstable . . . It will rise to a good comodity'. The 'stranger' was probably Cornelius Stevenson, another Brabanter who was granted the monopoly to produce copperas at Whitstable in 1565 but did not begin production at that time.

In the same year, a third Brabanter, Cornelius De Vos, took over Kendall's unproductive monopoly and initiated copperas production in Dorset, with Cornelius Stevenson named as the leaseholder.

Various transactions illustrate the great value of copperas during this period. For example, in 1584, a 100-ton cargo bound for London in 1584 realised the huge sum, for the period, of £1,200. However, domestic copperas production in Dorset was soon superseded by the south-eastern industries, which benefitted by their proximity to the ever more important London markets.

Whitstable industry

The first copperas production probably began in Whitstable in 1588, when Cornelius Stevenson's name first appears in the Whitstable lay subsidies - parish records detailing the giving of money to the poor - one year after his lease in Dorset ran out. The first two Whitstable works, apparently situated on coastal flats, were soon lost to the sea but were quickly replaced by works situated on higher ground inland.

It is likely, given their position on the foreshore, that the remains of copperas beds excavated in the late 1990s by the Canterbury Archaeological Trust were parts of these works. What we found were the remains of five troughs made of wooden planks, connected by mortice and tenon joints, and lined with clay. Further remains along the shore were interpreted as forming part of the same structure, suggesting an overall length of at least 140ft.

Chalk rubble, fragments of brickwork and iron remains found on site were all consistent with a description of copperas works written in 1677: 'They make Beds . . . about an hundred feet long, fifteen feet broad at the top, and twelve feet deep, shelving all the way to the bottom. They ram the Bed very well, first with strong Clay, and then with the rubbish of Chalk . . .'

Superimposed over the top of the copperas beds at Whitstable were a series of timber posts arranged in triangles. They are shown on a chart dated 1725 and may have supported a raised work surface to allow copperas production to continue despite rising sea levels. In 1693 a stockpile of 300 tons of iron pyrites in a Whitstable warehouse caught fire and burned for a week. Despite such set-backs, by about 1763 Whitstable had six works and was the biggest copperas producer in Britain. Maps show nine buildings associated with the industry in 1725, and ten by 1770. But after that, decline set in.

Terminal decline

In 1775, a Whitstable copperas works owner paid for a massive system of sea defences to protect the site from rising water levels, including large mudstones used as infilling. A number of these stones were found during the excavation. The work was in vain. Six copperas houses existed in 1798 but a map of 1835 shows only one building. A contemporary description states: 'Near the sea shore, the manufacture of copperas was formerly carried on . . . but nothing is now remaining but a few ruinous buildings'.

The chemical industry lacks charm and we take the role of such mundane chemicals as detergents, adhesives, textile dyes and fertilisers for granted, as if they had come into being spontaneously as part of our industrialised society. There is no doubt that the study of their history has been much neglected in favour of the heavy industries such as iron, steel, coal and steam, now seen as tinged with romance.

But with the rediscovery of copperas, the crucial importance of the chemical industry to Britain's economic development can now, perhaps, be better understood.


A combination of water and air has a remarkable chemical effect on the metallic fossils known as copperas stones. If you pick one up, wet, and put it in your pocket, it will have burned a hole in the material within three hours. It will be hot to the touch.

This natural chemical reaction formed the first part of the copperas manufacturing process in the 16th-18th centuries. Copperas stones (FeS2) were collected and placed in troughs on the foreshore. There the stones, washed by the sea, would oxidise and be colonised by bacteria. After about four years, they produced 'liquor' - a dilute solution of hydrated ferrous sulphate (FeSO4.7H2O) and sulphuric acid (H2SO4), which flowed via a planked channel to a cistern.

The Deptford cistern of chalk-caulked oak boards was subdivided to reduce loss from leaks. One Whitstable cistern measured 15 feet by 6 feet, one measured 80 feet by 9 feet and one 60 feet by 9 feet. However, in the earliest Whitstable works, liquor was pumped into '18 greate butts', probably sunk into the ground as shown in a print in the German writer Agricola's De Re Metallica (1556). At Queenborough, the liquor was conveyed to old barrels, then to 'a great tub'.

From the tub or cistern, the liquor was taken to a boiler where the liquid was concentrated and reduced. At Deptford, the boiler measured 8 feet square and at Whitstable one measured 12 feet square. The copperas boiler was raised above one or more furnaces by a grid of iron bars suspended between brick walls. The boiling process, fuelled using Newcastle or Sunderland coal, lasted about 20 days and required immense quantities of coal. The Queenborough works consumed 300 tons annually up to 1640, and Whitstable received about 13,250 tons of coal yearly from Sunderland in the late 18th century.

About 100lb of scrap iron was placed in the boiler before the introduction of the liquor and a further 1,500lb was added later, along with more liquor to stop the boiling solution becoming too dense and acidic and melting the boiler. The reason for adding iron was to convert the sulphuric acid (H2SO4), condensed through the boiling process, into copperas (FeSO4).

The strength of the liquor was tested by pouring small quantities into a small pan and observing how long it took to crystallise. When sufficiently concentrated, the liquor was conducted into a cooler, where it remained for about 14 days. The coolers often contained rods or branches to increase the surface area on which the liquor could crystallise.

The 17th century writer Cecilia Fiennes, in The Journey of Cecilia Fiennes 1685-1696, describes the process as follows: 'They place iron spikes in the panns full of branches so, as the liquid boyles to a candy, it hangs on these branches. I saw some taken up. It look't like a vast bunch of grapes, the coulleur of the Copperace not being much differing . . .'

Although usually of lead, in Deptford the cooler was made of tarras, a cement which, like lead, did not dissolve in the acidic solution.

Crystallised copperas in the cooler, or shaken from the rods, was shovelled onto a board, allowing any excess liquor to drain into a second cooler, along with any liquor left in the first cooler, for later reboiling. Saleable copperas was shipped in barrels weighing roughly half a ton.

Tim Allen is Projects Director for Canterbury Archaeological Trust and a Lecturer at the University of Kent. He excavated the Whitstable copperas beds in the late 1990s. A detailed report, 'Copperas', will be published by CAT later this year.

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