Grace's Guide To British Industrial History

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Grace's Guide is the leading source of historical information on industry and manufacturing in Britain. This web publication contains 164,616 pages of information and 246,219 images on early companies, their products and the people who designed and built them.

Grace's Guide is the leading source of historical information on industry and manufacturing in Britain. This web publication contains 147,919 pages of information and 233,587 images on early companies, their products and the people who designed and built them.

Soho Mint

From Graces Guide
Boulton cutting-out press, as supplied to the ROYAL MINT
Boulton cutting-out press, ROYAL MINT
Boulton coining press, ROYAL MINT
Droz segmental collar

in Handsworth, Birmingham

Introduction

The Soho Mint was established by Matthew Boulton in 1788 to mass produce coins of high and consistent quality, thereby addressing two major national problems: coin shortages and widespread counterfeiting. It was the first steam-powered mint in the world.

The Mint reflected Boulton's technical ability, metallurgical knowledge, his experience as a manufacturer, ingenuity, enthusiasm for steam power, and ability to select and motivate the right people, and he personally addressed every aspect of the various processes. Unlike most of his other business ventures, he controlled the Soho Mint virtually single handed. He initiated and developed coining methods which were to revolutionise mints worldwide. He developed the technology and quality control necessary to produce millions of standardised coins. His coins, medals and tokens were widely exported.[1]

General

Before the mint was established, Matthew Boulton struck 100 tons of copper coins (blanks only?) at the Soho Manufactory in 1786 for the East India Company.

1788 Boulton approached the British government with a proposal for minting low value coins by powered machinery. This would help to alleviate the shortage of copper coins in Britain and would cost less. Samples were available in May although the first order from the government did not come for 10 years. Boulton built the first steam-powered mint, adjacent to his manufactory at Soho (grid reference SP051890) in Handsworth, near Birmingham.

Note: The Soho Manufactory, on the same site, was a separate enterprise, and Boulton & Watt's Soho Foundry was also a separate business, located 1 mile west of the Soho manufactory and Soho Mint. The Mint was owned exclusively by the Boulton family, and was run first by Matthew and then by his sons. They did make use of of Boulton and Watt's engineers and production facilities.

It was intended that his coins would be produced with minimal labour, and be superior to existing coins by having a high polish, being perfectly round, precisely uniform in diameter and thickness, with the images made exactly concentric to the edge, and having the faces stamped concurrently with the embellishment of the edges with an inscription or ornament.[2]. The images and the text would be artistically designed and engraved to the highest standards.

It should be emphasised that many aspects of the minting processes were improved, rather than originated by Boulton and his assistants. However, the application of steam power, the degree of automation applied, and the productivity acheived at the Soho Mint were unprecedented.

Boulton had recruited Jean-Pierre Droz from the Paris Mint in December 1786 to engrave dies for a new regal coinage issue. Droz had previously provided information on press design, and promised a new and improved design for a screw press and claimed to have a better method of multiplying dies. Dies had to be changed frequently, and an effective and economical method of reproducing them from a master die (multiplying) was vital. Droz also invented the segmental collar (virole brisée) for embossing the edges of coins. Droz did not arrive at Soho until October 1788, and he returned to France in June 1790, taking Soho’s new technological ideas with him. His supposed method of multiplying dies came to nothing. Boulton complained that: ‘He [Droz] is a quack and hath been only learning at Soho and not teaching; his only value is as engraver.' In 1802 Droz claimed to have invented what Boulton considered his own techniques.[3]. The working relationship between Boulton and Droz was examined in some detail by J. G. Pollard [4]. James Watt also wrote of Droz's shortcomings in 1790 (see Pollard's Paper) and in 1809[5].

In fact, some sources credit Francesco Comelli of the Bologna Mint with inventing a collar and ejection system to be used with a screw press, and Droz and Phillipe Gengembre with a method of feeding blanks into a press and placing them in the collar, and ejecting after coining the piece, in one cycle while the press was manually operated.[6] [7]

In 1793 Boulton hired German engraver Conrad Heinrich Küchler.

In 1790, Boulton learned of the die-engraving machine of Jean Baptiste Barthelemy Dupeyrat (1759-1834)[8] and obtained one for the Soho Mint. One source states that when James Watt, he took one of these machines with a view to improving it.

Refined copper was bought in from a variety of suppliers and rolled to the required size by Boulton, who wrote: Copper, when hot, rolls very soft & easy, in comparison to what it doth when cold. It is sufficiently hot roll’d when it becomes equal to twice the thickness of the coin intended to be made. ....I shall rolle it twice in fine polished rollers, ... rolle it again twice in finer rolls, ... but previous to the last rolling, I guage it by my new invented calliper & in the last time passing the rolls bring it very exact to the proper thickness. [9].
It would be interesting to know more about Boulton's measuring calipers. Sue Tungate provides a great deal more information about the various process of rolling, pickling and cleaning the copper during rolling, even down to the fact that Boulton supplied his workers with gloves to avoid putting greasy fingermarks on the copper. Gloves were initially ordered from Robert Blood.

Sue Tungate highlights the considerable efforts taken by Matthew Boulton to obtain and to process steel suitable for the production of reliable and hard-wearing dies. Cooper[10] also supplies information about the material in the broader context of the history of coinage dies. Problems had resulted from the presence of slag inclusions in the cast steel ingot. These tended to congregate at the top and in the centre of the ingot, and remained in the bars forged from the ingot. Boulton had the bars forged square, cut into short slugs, and forged into a conical shape, with the central axis normal to the axis of the original bar. In this way the engraving was done on a face less likely to contain inclusions. This practice was used in mints for the next 150 years.

A double-acting rotatory steam engine was installed in the mint in 1788. The new steam-powered press was tested during 1789 and 1790.

The coin blanks were cut out of the rolled strip by presses driven by the new steam engine. The blanks were 'tumbled' to remove the sharp edges.

Business in manufacturing coins, medals, tokens and mint machinery came from the colonies and elsewhere.

The improvements developed at the Soho Mint were introduced into the Royal Mint, at Tower Hill, which was constrncted in 1810. Boulton and Watt furnished the steam engines and the coining machinery, while the rolling machinery was supplied by Rennie, and Barton's equalizing machinery was constructed by Maudslay. Similar eqipment was supplied to mints at St. Petersburg, Copenhagen, Calcutta, and Bombay.[11]

A grand total of 600 million coins and medals were struck by the Soho Mint.

1809 After Matthew Boulton's death, the Mint was directed by Matthew Robinson Boulton.

1841 MRB's son Matthew Piers Watt Boulton took over management of the Mint from his father until he closed it in 1850.

1850 On 1 April, the auction was announced of equipment from the defunct Soho Mint.

There are no remains of the Soho Mint or the Manufactory to be seen above the ground.

In 1860 James Watt and Co decided to establish a new mint at the Soho Foundry, named the Soho Foundry Mint, but sometimes confusingly referred to as the Soho Mint. In 1850 James Watt & Co had bought one of the old Soho Mint presses, and this was installed at the new mint at the end of a row of 12 new presses.[12]

George Selgin examined aspects of Boulton's acheivements and found that 'Boulton’s presses allowed him to make high quality and perfectly round coins faster than was possible by manual means, they did not enable him to produce coins that could not also be produced manually. On the whole, steam presses were somewhat less versatile than manual ones. ..... And although counterfeit-resistant coins could be produced using manual labour, Boulton did, after all, play a crucial role in solving Britain’s small-change problem. He did this, not by demonstrating that steam presses were capable of making uniquely counterfeit-proof coins, but by hiring the world’s best engravers, by employing improved coin designs, by striking coins in collar, and by mastering the art of die production and multiplication. Most of all, though, he did it by managing to secure a series of regal coinage contracts despite the Royal Mint’s opposition, thereby showing the Mint that its coinage ‘prerogative’ was not absolute — that, if it would not make good regal coins, someone else might. By managing to encroach upon the ‘old shop’s’ monopoly, Boulton forced it to mend its medieval ways.'[13]

The Presses - Illustrations

Various illustrations of cutting-out presses and the coining presses at the Soho Mint are included in the Demidowicz book, but in some cases there is uncertainty about the extent to which these represented the 'as-built' machines at any particular time in the Mint's history. The illustrations included above relate the the Royal Mint unless otherwise stated, and are believed to accurately represent the machines used there for many years.

The Presses - General

Matthew Boulton's Cutting-out (Blanking) Presses and Coining Presses show a degree of sophistication which is difficult to reconcile with 18th century industrial machinery. They were screw presses, but unlike those traditionally used, they did not rely on men to provide the motive power. The traditional screw presses (fly presses or balanciers) for coining demanded the vigorous action of teams of men, to a degree depending on the size of coin to be squeezed in the dies. Boulton's coining presses would use power derived from a steam engine and each would be attended by just one boy, with the occasional attendance of a skilled man to undertake maintenance, adjustments, and resetting when dies were changed. Of course, the steam engine and boilers had to be constantly attended.

Compared with traditional man-powered presses, the method of applying the mechanical/pneumatic power offered the prospect of greater consistency in the stamping force.

It is not difficult to find illustrations of these machines, but it is difficult to find adequate descriptions, particularly of the coining presses. George Frederick Ansell provided a comprehensive, but not entirely comprehensible description of the Boulton presses installed at the Royal Mint. Cutting-out press illustration and description here. Coining press illustration and description here.

Description and 1818 illustration in the 1824 Encyclopaedia Britannica Supplement here

H. W. Dickinson provided illustrations and a description of the coining press based on Boulton's Patent of 1790. However, Cooper[14] believes that the presses illustrated were used for blanking only, and not for coining, which was done by more complex presses, which, he believes were not patented. Further, he states that 'The evidence appears to show, that in 1797, seven years after taking out the coining press patent, the cart-wheel penny and twopenny pieces were produced on manually operated screw presses'. Was this because of the large size of those coins, putting them beyond the capacity of the powered presses?

The situation is further complicated by the fact that the drawings of the Royal Mint's Boulton presses show appreciable differences between the cutting-out presses and the coining presses, the latter being more complex and having more massive frame castings. The actuation mechanism is also more complex on the coining presses. The cutting-out presses, arranged in a circle, were driven by a single large horizontal cam wheel. This raised the dies and at the same time raised a piston which created a partial vacuum beneath itself. Atmospheric pressure acting on this piston was then used to provide the torque to bring the cutting-out die down. The London Mint coining presses had no cam wheel, and obtained their motive power from a vacuum chamber, the vacuum being created by a steam engine. George Demidowicz's book contains a number of drawings of presses at Soho, and these all show a consistency in the shape of the press frame, and that shape is consistent with that of the London Mint's coining machines, and not with their cutting-out presses. The following may be relevant:-

At the end of January 1788, two small and two large presses were being prepared, and by 5 February 'four more Presses for cutting out' had been ordered.[15]. Were the small presses the cutting-out presses, and the large presses the coining presses.

The first layout sketches (January and July 1788) showing the proposed location of the presses at Soho shows horizontal rod connecting the presses in rows, with ‘the strokes of the presses produced by the alternate opening & shutting of the communications of the air pump with the engine & with the atmosphere.', but a 1789 sketch by Boulton shows eight presses arranged in a circle.

It appears that the use of a purely vacuum-based system to power the coining presses, without an engine-driven cam wheel, was proposed and developed by John Southern in 1798, and came into operation in March 1799.[16]

Press Operation - Turning the Screw

Up to point, the presses worked on the same principle as the traditional fly presses, in which the 'fly' arm is swung to give it momentum and turn the screw to impress the coin between the dies. The energy not transferred to the coin or lost in friction is available to make the fly rebound.

Boulton's presses did without the manpower, and initially used a combination of mechanical power - provided by a steam engine - and . Under the 1790 patent, A number of presses were arranged in a circle around the axle of a large vertical shaft. The engine-driven shaft turned a large horizontal cam wheel which contacted an arm on each press, rotating the screw to raise the upper coining die above the lower die. At the same time a pair of arms attached to the screw pulled chains which raised the pistons of four cylinders, creating a vacuum below the pistons. The atmospheric air pressure acting on top of these pistons was then available to pull the chains and thereby rotate the fly press screw when released by the cam wheel, stamping the coin.

This was the basis of the system provided for the cutting-out presses at the Royal Mint, although the details were very different. See illustration here. The presses worked at a rate determined by the speed of the engine. The strip for blanking was fed under the punch manually. An interesting detail on the Royal Mint's cutting-out presses was the use of a toothed coupling between the screw and its actuating shaft (see 'Q' in first illustration above), similar in principle to the 20thC Hirth coupling.

The coining presses were more complex, and the magnitude of the applied force was more critical. By 1798 the operating principle had been considerably modified, evidently to that shown in the Royal Mint drawing, pp.58-9 here. The cam wheel was abandoned, and the operating force was entirely pneumatic, a vacuum cylinder applying the torque through rods and levers to the fly press screw. A steam engine raised the vacuum, evacuating the air from a manifold which served all the coining presses. In order to provide consistency of stamping force, it was presumably essential to maintain a constant vacuum in the manifold. However, different forces were required for different types of coin. Therefore an addditional system was provided, by which an upward (counter) force was applied to the main screw. This system featured a balance beam with adjustable weights and another vacuum cylinder applying force to the weighted end of the beam. The original balance beams were made of wood, but these were replaced by fish-bellied cast iron beams of T-section.

Demidowicz[17] provides a number of drawings from 1798 and 1825 relating to the vacuum-raising arrangements introduced during alterations at the Soho Mint at those periods. In the '1798' version the rocking wooden beam of the steam engine was linked to another beam, which worked a pair of reciprocating air pumps. The '1825' version had a 'six-column' engine whose crankshaft drove a two-cylinder air pump.

It would have been important to maintain a constant vacuum in the manifold. It would probably have been a straightforward matter to meet this requirement with a pressure governor, in which a piston or diaphragm responded to the manifold pressure to control the admission of steam to the engine. However, one of the 1825 drawings shows a flyball speed governor crudely sketched in.

A distinctive feature of these coining presses was a trumpet-shaped torque-tube with its flared end attached to the top of the fly arm, and its top end passing through the ceiling. At the top, just above the upper floor, was the lever arm connected to the main vacuum cylinder via rods and levers, applying the torque, while a slender rod and swivel joint rose up through the trumpet the connect with the cast iron balance beam.

Note: The basic shape of the coining press frame continued to be used for many years, despite changes to the method of applying the stamping force. The Calcutta Mint ordered coining presses c.1860 which were to incorporate a pneumatic cylinder to rotate the screw. The arrangement was proposed by Mr A. Harvey of the Calcutta Mint, and the detail design was done at Soho. Trial operation proved to be unsatisfactory, and the company was paid to convert the presses to the conventional arrangement.[18]

Coining Press Design - Influences?

The question arises about the extent to which Droz was involved in the design of the Soho coining presses.

In 1791 Boulton wrote that 'we have 6 presses cast from the design of Droz model ...'. Shortly before that he wrote that Droz had requested him to send an unfinished press.[19].

Pollard states that, as far as the coining presses were concerned, Boulton had expected Droz to furnish designs and models incorporating his improvements, which seem principally have been the six-part segmental collar and the mechanical means of ejecting the struck coin from the dies. There is also mention of Droz's fine screws. On 14 April 1788 Boulton acknowledged the safe arrival of the plaster model of Droz's press. This implies that Droz's contribution to the press design was not limited to the ejecting system and the collar.

Tungard also shows that Droz's input extended to the screws, noting that 'Anthony Robinson was making the screw for the large press and Bullock the smaller ones, to designs sent by Droz.', and 'I now wait for his opinion respecting the best mode of casing [casting?] the female screw in Brass'. [20]

If we now consider the appearance of the coining presses, we see a strong similarity in the 'architectural form' of the presses made by Droz and Boulton. Specifically, the columns of the casting partly terminate with square corners, and partly continue up to merge with the heavy central boss at the top, the transition being in the form of a semi-elliptic arch, with a central 'keystone' feature. We see this here in a drawing of a Droz coining press, and in all the illustrations of Boulton's coining presses - including Boulton's 1790 patent drawing, and in two surviving Droz presses in the Monnaie de Paris. The Droz press drawing also shows a very similar blank-placing device to that used by Boulton. These similarities do not help with the question of who influenced whom, because the Droz drawing and the presses all date from after his falling-out and departure from Soho.

Regardless of the originator of the 'architectural' design, there are significant differences between the Boulton and Droz coining presses. Most obvious is that Droz continued to use the traditional balancier or pendulum swung by a team of men to apply the stamping force, whereas at Soho manpower was replaced the self-acting vacuum-operated system, using a steam engine to create and sustain the vacuum. A more subtle difference was in the arrangement of the main press screw. It appears that in the Droz press shown in the post-1800 drawing, the screw was 'self-guided' by the threaded portion to keep it central and vertical, whereas in the Soho press the threaded portion determined the vertical position, while the centrality and vertical guidance was determined by having cylindrical journals immediately above and below the threaded portion, these running in guide bushes which each could be adjusted transversely by four screws. The 1794-6 Droz coining press in the Monnaie de Paris has a different, more conventional arrangement, the transverse guidance being provided by a large crosshead. However, there is a proviso concerning the Boulton presses, which arises because of uncertainty about the chronology of any design changes. The best Soho press drawing known to exist is a coloured sectional arrangement drawing dating from 1850 and relating to one of the Soho Mint coining presses before it was moved to the Soho Foundry. This clearly shows the screw guided by journals top and bottom. Another drawing of a coining press, by John Phillp, c.1799, shows no exposed thread, suggesting that it also has guiding journals. A third drawing by John Phillp, 1797, and said to represent a 1788 press, shows and exposed screw thread at the top. It also has cam-follower arms, which might indicate either that it is a cutting-out press, or that it represents a 'first generation' coining press. All three drawings are included in Demidowicz's 2022 book.

It is not clear to what extent Soho used the segmental collar. Such detail drawings as are available for coining presses at Soho and at the Royal Mint show a simpler ring collar, into which the blank was pushed. Levers kept the ring level with the surface of the die until the upper die descended. On release, a three-leafed spring caused the ring to rise, so that as the blank was struck, it was surrounded by the collar. James Lawson is credited with this arrangement. [21]

Location

Matthew Boulton's grand house, Soho House was set in landscaped parkland just two miles from the centre of Birmingham, and this is where he built the Soho Manufactory and then the Soho Mint. For reasons of security, the Mint was built in the garden of Boulton's Soho House. In fact the first Mint buildings were located immediately behind a group of estate buildings which included Boulton's menagerie, tearoom, fossil room and laboratory.

Water power was available to the manufactory thanks to the Hockley Brook, which passed through the estate and supplied a mill pond - Soho Mill Pool - which provided a head of water for a waterwheel installed in the north end of the Manufactory complex. This powered a number of polishing laps and a set of rolling mill stands. This arrangement was inadequte for the requirement for rolled copper strip for the Mint, and in 1788 it was decided to add a rotatory steam engine. This would drive the laps and also power machines for cutting the blanks from the strips for coining. The waterwheel would then be free to drive the rolling mills and some other coining-related activities. The number of roll stands was to be increased from three to five, and five cutting-out presses were to be installed in the gallery of the rolling mill. However, drawings dated late 1788 show the presses arranged in a circle above the lap engine and driven by it. Even then, the power available for rolling was insufficient for the number of roll stands.[22]

New Mint buildings were constructed in 1791, but a period of slackness ensued.

Engravers

Initially Boulton relied heavily of engravers from the Continent, but Tungate points out that many of the well known die engravers in Birmingham and elsewhere were first employed or trained at Soho Mint. These included John Gregory Hancock, who was apprenticed to Boulton in 1765, and in turn, John Stubbs Jorden was apprenticed to Hancock; members of the Wyon family, including George, Peter and Thomas; another former pupil at Soho was Thomas Halliday, who in turn had William Joseph Taylor as an apprentice in 1818; Sir Edward Thomason was apprenticed at Soho in 1786. In his memoirs he recollected: I was initiated in this scientific school at Soho which induced in me a versatility of taste for mechanics and to cultivate the arts and sciences ..... Having been accustomed .... at Soho to witness continuous new inventions in mechanisms and metallurgy, the mind becomes restless to produce some novelty of invention worthy of being patented. [23]

1850 Sale

Matthew Piers Watt Boulton did not share his father's enthusiasm for the Mint, and decided to close it. The machinery in the Soho Mint and the mint-related machinery in the Soho Manufactory was put up for auction in 1850.

1850 'During the past week Messrs. Fuller and Horsey, auctioneers of London, have been engaged in disposing of the machinery, dies, coins, and medals of the Soho Works, near this town. The auction commenced on Monday last, by direction of the executors of the late Mr. Boulton, and was continued daily until Friday evening, when it closed with the 707th lot. The well-known celebrity of the Mint and other departments of the manufactory attracted a great concourse of machinists and others to the sale, and the competition for many articles was very spirited. The collection of dies was secured principally for Sir George Chetwynd, and Mr. Makepeace, who, it is presumed, represented Mr. Boulton. Some of them were afterwards re-purchased for France. The coining presses sold low, the highest prices being 75l. for lot 9 consisting of a press, highly finished, with 5 1/2-inch bright screw to rise 5 inches at one revolution, with steel plug, brass-box, 18 inches deep, cast-iron fly, and cast-iron balance-beam, 12 feet long. Lot 202, consisting of 119 medals and coins, struck at the Mint bronze, and including representations of the Emperor of Russia, Execution of the King of France, Queen Charlotte, tbe Battle the Nile, Lafayette, Rousseau, &c, sold for 6l. ...... Lot 341, a portable condensing steam-engine, 12-horse power, by Boulton, Watt, and Co., 185 guineas, purchased for Mr. Wilkes. Lot 549, a powerful medal, or multiplying press, purchased by Mr. Lingard, for 19l. 7s. The tools and machines sold well, considering the antiquity of their construction. The pumping engine, "Old Bess," the first constructed by James Watt, realized 52l. 10s.; purchased by Mr. S. Walker. This engine is a perfect curiosity, the piston-rod was made from broken Redditch needles, purchased by Mr. Watt for that purpose. Mr. Walker also bought another engine. The rolling mills and rolls were purchased by a London house for from 5l. to 12l. per pair. The present firm of James Watt and Co., purchased one of the coining presses and appendages.'[24]

Some of the machinery was bought at auction by the new Birmingham Mint of Ralph Heaton II.

Recent Detailed Accounts

2010: A thorough study of the successful development by Matthew Boulton of the Soho Mint and its improved processes was undertaken by Sue Tungate for her PhD thesis, which is available online [25]

2022: The book 'The Soho Manufactory, Mint and Foundry, West Midlands' by George Demidowicz provides a comprehensive and profusely illustrated analysis of the Soho factories [26]

See Also

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Sources of Information

  1. [1] 'Matthew Boulton and the Soho Mint: Copper to Customer'. Ph.D. Thesis by Sue Tungate, 2010, p.4
  2. [2] 'Matthew Boulton and the Soho Mint: Copper to Customer'. Ph.D. Thesis by Sue Tungate, 2010, p.127, note 493
  3. [3] 'Matthew Boulton and the Soho Mint: Copper to Customer'. Ph.D. Thesis by Sue Tungate, 2010, pp.120, 123, 165, 166
  4. [4] MATTHEW BOULTON AND J.-P. DROZ by J. G. Pollard, The Numismatic Chronicle (1966-) Seventh Series, Vol. 8 (1968), pp. 241-265 (25 pages), Published by Royal Numismatic Society
  5. Memoir of Boulton by Watt, 1809. Reproduced by H. W. Dickinson in 'Matthew Boulton', 1937, Cambridge. See Appendix I
  6. [5] Newman Numismatic Portal, drawing on An Encyclopedia of Coin and Medal Technology For Artists, Makers, Collectors and Curators, compiled and written by D. Wayne Johnson, Roger W. Burdette, Editor
  7. [6] 'Matthew Boulton and the Soho Mint: Copper to Customer'. Ph.D. Thesis by Sue Tungate, 2010, p.169
  8. [7] Coin and Medal Die Engraving Part 2 – Matthew Boulton: March 21, 2011 by medalblog
  9. [8] 'Matthew Boulton and the Soho Mint: Copper to Customer'. Ph.D. Thesis by Sue Tungate, 2010, p.133
  10. Denis R. COOPER (1995) The Development of Coinage Dies from Bronze to Steel, Transactions of the Newcomen Society, 67:1, 91-108, DOI: 10.1179/tns.1995.004
  11. The Mechanics Magazine, Museum, Journal and Gazette, Vol XLVI, 1847, p.85
  12. 'The Soho Manufactory, Mint and Foundry, West Midlands - Where Boulton, Watt and Murdoch made History' by George Demidowicz, 2022. Liverpool University Press for Historic England, pp.123-5
  13. 'Steam, hot air, and small change: Matthew Boulton and the reform of Britain’s coinage' by GEORGE SELGIN, Economic History Society 2003: Economic History Review, LVI, 3 (2003), pp. 478–509
  14. DENIS R. COOPER (1974) The History and Development of the Coining Press, Transactions of the Newcomen Society, 47:1, 59-72, DOI: 10.1179/tns.1974.005
  15. 'The Soho Manufactory, Mint and Foundry, West Midlands - Where Boulton, Watt and Murdoch made History' by George Demidowicz, 2022. Liverpool University Press for Historic England, p.91
  16. 'The Soho Manufactory, Mint and Foundry, West Midlands - Where Boulton, Watt and Murdoch made History' by George Demidowicz, 2022. Liverpool University Press for Historic England, p.101
  17. Demidowicz, 2022, pp.105 & 113
  18. The Engineer 17 Dec 1909
  19. 'The Soho Manufactory, Mint and Foundry, West Midlands - Where Boulton, Watt and Murdoch made History' by George Demidowicz, 2022. Liverpool University Press for Historic England, p.98
  20. [9] 'Matthew Boulton and the Soho Mint: Copper to Customer'. Ph.D. Thesis by Sue Tungate, 2010, pp.123-4
  21. [10] 'Matthew Boulton and the Soho Mint: Copper to Customer'. Ph.D. Thesis by Sue Tungate, 2010, p.169
  22. 'The Soho Manufactory, Mint and Foundry, West Midlands - Where Boulton, Watt and Murdoch made History' by George Demidowicz, 2022. Liverpool University Press for Historic England, pp.21-3, 53-59
  23. [11] 'Matthew Boulton and the Soho Mint: Copper to Customer'. Ph.D. Thesis by Sue Tungate, 2010, p.247
  24. Aris's Birmingham Gazette, 6 May 1850
  25. [12] 'Matthew Boulton and the Soho Mint: Copper to Customer'. Ph.D. Thesis by Sue Tungate, 2010
  26. 'The Soho Manufactory, Mint and Foundry, West Midlands - Where Boulton, Watt and Murdoch made History' by George Demidowicz, 2022. Liverpool University Press for Historic England
  • [13] Wikipedia
  • The Lunar Men, by Jenny Uglow, Faber and Faber, 2002