Posted in Archaeology, Bringing Alive The Past, History, Museum

The Cast Iron Cooking Pot That Changed The World – Ironbridge, Shropshire

Cooking pot from the Coalbrookdale Museum of Iron, Ironbridge, Shropshire. Image by courtesy of Ironbridge Gorge Museum Trust
Cooking pot from the Coalbrookdale Museum of Iron, Ironbridge, Shropshire. Image by courtesy of Ironbridge Gorge Museum Trust

A short while ago, I received a Press Release from PR Matters that was so exciting, I just had to share it with you here. New research, conducted by retired 18th and 19th century metallurgist Dr Richard Williams, has proved that a cooking pot in the collection of the Ironbridge Gorge Museum Trust is the oldest known coke iron casting in the western world.

Without using coke to smelt iron, there would have been no Industrial Revolution; the supply of wood was simply not extensive enough. It has previously been assumed that Abraham Darby I (1678-1717) invented the process because wood was already becoming increasingly scarce and coke was therefore generally more economic, but Dr Richard Williams has established that it was, in reality, all about cooking pots.

Dr Williams has been working on behalf of the Ironbridge Gorge Museum Trust as a member of the museum’s Birmingham Advisory Group. The work, published in the journal Historical Metallurgy shows that Abraham Darby’s genius was more commercial than technical (as previously thought) and that he actually first smelted iron with coke, as opposed to charcoal from wood, for just one application.

Working on behalf of the Ironbridge Gorge Museum Trust, he comments on what was primarily a technical analysis: “We have now shown how Abraham Darby was the first man to make a profitable business from smelting iron with coke rather than charcoal. He saw an opportunity that no one else did, applied for a patent to protect it and got on with creating the business to exploit it.”

©Ironbridge Gorge Museum Trust. An extract from Abraham Darby I's original 1707 patent for casting iron bellied pots.
©Ironbridge Gorge Museum Trust. An extract from Abraham Darby I’s original 1707 patent for casting iron bellied pots.

In 2013, I want on an incredible press trip to Ironbridge, Shropshire. I cannot tell you what an astonishing heritage site it is. There are 36 scheduled monuments and listed buildings cared for by The Ironbridge Gorge Museum Trust, spread over a 6 square kilometre site.

The Trust also operates 10 museums which collectively tell the story of the birthplace of the Industrial Revolution. These museums are: Blists Hill Victorian Town; Enginuity; Coalport China Museum; Jackfield Tile Museum; Coalbrookdale Museum of Iron; Museum of The Gorge; Darby Houses; Tar Tunnel; The Ironbridge and Tollhouse and Broseley Pipeworks. For anyone interested in social or living history, Ironbridge is a must!

The cooking pot which has been the subject of Dr Williams findings, is part of the Coalbrookdale Museum of Iron collection. The unique cast iron pot, dated 1714, inspired Dr Williams to wonder how it had been cast in order to have exactly the right metallurgical structure? He saw the relationship between the only patent (see image above) that Abraham Darby filed – about moulding such pots in sand – and his modified blast furnace.

©Ironbridge Gorge Museum Trust. Diagram of the old Furnace, Coalbrookdale. The Furnace went out of use in 1818 but the foundry buildings around it remained in use and even expanded to enclose the remains of the furnace.Diagram of the old Furnace, Coalbrookdale. The Furnace went out of use in 1818 and the foundry buildings around it remained in use and even expanded to enclose the remains of the furnace.©Ironbridge Gorge Museum Trust ©Ironbridge Gorge Museum Trust. Diagram of the old Furnace, Coalbrookdale. The Furnace went out of use in 1818 but the foundry buildings around it remained in use and even expanded to enclose the remains of the furnace.
.Diagram of the old Furnace, Coalbrookdale. The Furnace went out of use in 1818 and the foundry buildings around it remained in use and even expanded to enclose the remains of the furnace.©Ironbridge Gorge Museum Trust

It had been previously thought that the two inventions were entirely independent, but Dr Williams realised that Darby’s patent would only work if the liquid iron he used to pour into his moulds was made with coke.It would not have worked with the previously universally used charcoal.

Darby’s new process was much cheaper than the competitive one, which was most effectively practised on the continent, with a consequently large importation of pots into England. On the continent they used charcoal but, in order to get the right structure in their iron, Dr Williams recognized that they had had to pour their metal into moulds that were very hot, thus being obliged to use an expensive moulding process where the sand grains were bound together with clay, the so-called loam process.

Darby’s patent specifically said that he was going to use no clay and his moulds could thus not be heated. Dr Williams explains that to make most castings, the composition of the iron had to be such that a grey structure resulted rather than a white one, but this was much more difficult when the casting was thin, as with a pot, because the metal cooled more quickly than with a thicker casting.

The iron had to be high in silicon to come out grey, something that was very difficult to achieve using charcoal. But coke did it much more easily and this Abraham Darby already knew, from the work of others before him. He clearly knew it some years before he first set out to make iron himself, because his patent was published in April 1707 and he did not start his coke blast furnace until the end of 1708.

It has not previously been realised – at least in the UK – that moulds used to be regularly heated. Dr Williams could find no reference to it in the English language.  There are however many references to it in the French encyclopaedias published in the second half of the 18th century, of which the Encyclopédie of Diderot is the most famous.

To prove his thesis, Dr Williams examined a number of 17th and 18th century pots made with the loam process at the Maison de Metallurgie in Liège.  He deduced that all pots bear characteristic markings that establish how they were made and in his paper he demonstrates that the pot in the Ironbridge Gorge Museums, dated 1714 (just six years after Darby’s first blast furnace came on stream) must have been cast using an iron made with coke. With no one else known to be making coke iron at the time, it could only be a genuine Abraham Darby product, the oldest known coke iron casting in the western world.

To begin with, coke iron was only of economic use for the manufacture of cooking pots, but the profit from this activity allowed him and his descendants the time to develop the coke blast furnace for all the other applications for which it became suitable. His first furnace produced just four tons per week.  In the world today, more than one billion tons of iron comes out of coke-fired blast furnaces each year.

Abraham Darby I – The Coalbrookdale Company

The Coalbrookdale Company was formed in 1709 by Abraham Darby I (1678-1717), an iron-master who had moved to the region from Bristol in the previous year. His original intention was to lease an ironworks with a view to setting-up a brass foundry – he had been experimenting with making brass pots since 1707 which led to his patent for casting iron bellied pots in dry sand.

He leased the Furnace at Coalbrookdale in 1709 from landowner Basil Brooke of Madeley and his wife Elizabeth, beginning blasting in January of the same year. Until the latter part of the 18th century, the most important industry in the Ironbridge Gorge was coal-mining – the first step on the road to the birth of the Industrial Revolution in the region.

Other coal-using industries utlising the area’s rich natural resources were: lead smelting; tar boiling; pottery making and brass manufacturing. The Tar Tunnel at Ironbridge is open to the public and well-worth a visit. In 1787, miners digging in the area struck a spring of natural bitumen (treacle-like black liquid) which has seeped out of the walls and formed into puddles for over two hundred years. It was money from coal that funded the first ironworks in the area.

Although now a haven of tranquillity, in the 18th and 19th centuries, the area resembled Dante’s Inferno, a scene which artist Philip James De Loutherbourg (1740-1812) captured so brilliantly in his iconic painting Coalbrookdale by Night (1801).

©Ironbridge Gorge Museum Trust. Iron Works at Coalbrookdale by Philip James De Loutherbourg (1740-1812) from an engraving by William Pickett. ©Ironbridge Gorge Museum Trust. Iron Works at Coalbrookdale by Philip James De Loutherbourg (1740-1812) from an engraving by William Pickett. De Loutherbourg was a theatrical designer who worked for playwrights such as R.B. Sheridan (1751-1816) and David Garrick (1717-1779). His painting, Coalbrookdale by Night (1801), depicting the raging Bedlam Furnaces in Madeley Dale, Shropshire, a little further downstream from Ironbridge, recreates the iconic scene of fire and brimstone that we now associate with the birth of the Industrial Revolution in Great Britain.
Iron Works at Coalbrookdale by Philip James De Loutherbourg (1740-1812) from an engraving by William Pickett. ©Ironbridge Gorge Museum Trust. De Loutherbourg was a theatrical designer who worked for playwrights such as R.B. Sheridan (1751-1816) and David Garrick (1717-1779). His painting, Coalbrookdale by Night (1801), depicting the raging Bedlam Furnaces in Madeley Dale, Shropshire, a little further downstream from Ironbridge, recreates the iconic scene of fire and brimstone that we now associate with the birth of the Industrial Revolution in Great Britain.

Between 1755 and 1780 the iron industry was booming in the region and five new groups of furnaces were set up:

The three surviving groups of iron furnaces mark these different phases in the local iron industry – the earliest, the Darby Furnace at Coalbrookdale …… Bedlam Furnaces (begun 1756-7) were the first of the great new Industrial Revolution furnaces, experimenting with new forms of power, while the Blists Hill Furnaces, begun in c.1832 and closed in 1912, signal the move away from water as a source of power, and eventually the end of smelting in the Gorge.

(Ironbridge Gorge by Catherine Clark, 1993, p.36, published by B. T. Batsford Ltd)

The Darby family were Quakers but did not force their religious beliefs on the workers at Coalbrookdale. The Darbys were known to be good employers as well as savvy business people, their workers rarely went on strike. Education, for both boys and girls, was also important to Quakers – a forward thinking approach for the time:

..adhering strictly to the ideals of self-discipline, frugality and simple faith, attitudes which extended into the conduct of their business. As members of the Society of Friends, Quakers formed a close-knit group, distinct in their way of dress and habits, and tending to socialize as a group. Many of the visitors who came to Coalbrookdale were Quaker associates, and the large houses at Coalbrookdale became a focus for this society.

The houses were built close to the works, but looked out over a more pleasant view of trees, pleasure gardens and a pool with a small decorative iron bridge.  For most of their history the houses were occupied for relatively short periods by family members or by works managers; often, as in the case of Abraham Darby III, while they built or altered finer houses elsewhere in rural settings.

Carpenters Row is an example of company housing: built c.1783, it is a terrace of eight cottages, each with a downstairs parlour with a range, a tiny pantry and a bedroom above….Carpenters Row would have provided a relatively good class of accommodation.

(Ironbridge Gorge by Catherine Clark, 1993, pp.40-41, published by B. T. Batsford Ltd)

Darby I’s son, Abraham Darby II (1711-1763), took over the running of The Coalbrookdale Company from his father in 1728. His contribution to the Company’s history is significant. He invented a method of making pig iron using coke which could then be converted into wrought iron:

The molten iron from a blast furnace could be poured direct into sand moulds to produce cast iron goods or cast ingots called “pig iron”. The pig iron was then either melted and cast in a foundry or purified to produce wrought iron that could be shaped by hammering and rolling in a forge.

(Extract from text panel at the site of the Old Furnaces, Upper Works, Coalbrookdale, Ironbridge Gorge Museum Trust).

For a more detailed overview of Ironbridge, below are links to previous articles I have written about various aspects of the site:

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