James Watts' father had invested in at least one known slaving voyage from Scotland. Some of the records mention the purchase and sale of Black people, e.g. Letter, James Hunter (St Eastatius) to James Watt of Greenock. 2 July 1740.

'Sir I wrote you from Sett Christophers dated the first of June leeting you know the badness of the market att Bass Stare..........

As negroes turn out dear Bought six three men and three women....'⁴

Money to develop the Watt steam engine came from diverse sources such as mine and plantation owners. Plantation owners wanted to find ways to make more money whether their interests were directly or indirectly related to slavery or slave trade activity. In 1795 Boulton and Watt & Sons established a foundry at Merry Hill, a mile from the Soho Manufactory (Handsworth) 'for the purpose of casting everything relating to our steam engines'.⁵ Inside the Soho Manufactory was the Soho Mint, which made coins, tokens and medals for such diverse purposes as commemorating the abolition of slavery, or money for the slave holding colony of Sierra Leone.

Boulton & Watt opened Soho Foundry in 1795 . Matthew Boulton and James Watt were businessmen and were keen to do business with West Indian plantation owners. They explored the prospect of selling steam engines to plantation owners in the Caribbean and in 1783 Boulton had entertained Mr Pennant, a notorious slave owner who owned huge estates in Jamaica and sought steam engines for his plantations there.

By 1825 Boulton & Watt had supplied Caribbean Islands with nearly 200 steam engines designed for sugar mills. Enslaved Africans cut the sugar cane, and operated the machines that crushed and boiled the juice from the sugar cane. The reason for harnessing steam power in boiling and purifying sugar is also to do with efficient working. Plantation owners were only interested in making money not in reducing the work of the enslaved. They were interested in inventions that increased productivity and profit. Slavery was not made redundant since cane still had to be cut by hand, and machines supplied with cane and operated, by enslaved Africans. Watt is on record as holding anti slavery views. Boulton never expressed any view on the matter of slavery.

Bolton and Watt were part of a network. In 1790 Samuel Galton recommended to John Dawson, a Liverpool-based slave trader, that he should contact Boulton and Watt and about supplying steam engines for Dawson's sugar works in Trinidad. The latter wrote to Boulton and Watt on 9 November 1790:

Sirs, I have been considering of the conversation Mr Galton & I had respecting the merits of the Steam Engine as I am going to have some Sugar Works erected in the Island of Trinidad & wish to have your Ideas & the opinion of experienc'd people how far it would be practicable to erect them on that plan: the want of Wind & Water the principle on which they are at present work'd, retards the progress so very much, particularly in crop time, That if an engine could be invented with a certainty of answering the purpose, the Rolers so contriv'd that if possible to have a greater effect in the pressing of the Cane than what is at present used but I must observe to you that without wood fire will answer the same purpose as coal, the undertaking would be very hazardous, Coals could not be laid in at that island for less than 71/6 pr Chaldron, the duty being 15/6.

I shall thank you to give me every information of the practicability of this scheme for could it be made to answer, a large field would be open in that quarter of the Globe, the King of Spain having granted a loan of a million Dollars to the Inhabitants of Trinidad for the purpose of erecting Sugar Works & purchase of Slaves which I am to have the supplying of. Should be happy to give every encouragement in the introduction of such a plan with yourself & I can engage the Governor will do the same.

Your reply will oblige Sir

John Dawson. ⁶

Watt, nevertheless was prepared to express view against slavery. On 31 October 1791, he corresponded on behalf of the firm of Boulton and Watt to Messrs Beguye & Co. of Nantes concerning the suspension of the production of their steam engine order following the outbreak of the slave revolt in the French West Indian colony of San Domingo (now Haiti). Watt wrote:

Gentlemen

The late unpropitious news from St. Domingo has made us suspend the prosecution of the order for your Engine until we hear from you. We have written to the foundery for that purpose & expect that no material expense has yet been incurred.

We thought it our duty to give you this information, to relieve part of your anxiety in case any fatal accident should have befallen your friend Mr. Bertrand.

We sincerely condole with the unhappy sufferers, though we heartily pray that the system of slavery so disgraceful to humanity were abolished by prudent though progressive measures.

We remain etc.

Boulton & Watt.⁷