Scheduled Monument
Grade II* Listed Building
The Bristol based brass industry was at the heart of advances in metallurgy in the 1700s, the processes being employed for the production of brassware comprising: copper smelting; calcining of calamine; alloying of copper and calamine to produce brass; distillation of zinc from calamine; production of brass by speltering; brass battery and rolling; and annealing of brass.
Closely linked to this
was the use of fuel, in particular developments which enabled the use of coal in preference to charcoal for the processing of metals. The scientific methods employed by the Bristol company were highlighted in the works of the Swedish scientist and philosopher, Emanuel
Swedenborg, who described a laboratory at Baptist Mills in his book “Opera Philosophica et Mineralis” ("Philosophical and mineralogical
works") published in 1734:
“A laboratory has been fitted up where they experiment on the different methods of converting copper into
brass. It contains a large number of assaying ovens and furnaces and the machinery works by flowing water. There is a
small hammer for testing how many blows the brass can endure without breaking; there are also teeth with which the brass is struck,
but only once at any one point.”
i. The Art of Converting Red or Rosette Copper into Brass by means of Calamine Stone. Messes Galon & Duhamel Du Monceau,1749
ii. L’Encyclopedie, ou Dictionnaire Raisonne des Sciences des Arts et
des Metiers. Diderot and D’Alembert. 1763
iii. The Bristol Brass industry: Furnace Structures and their Associated Remains,
Joan Day, Journal of the Historical Metallurgical Society 22/1, 1988
The collection of the Saltford Brass Mill Project includes three manillas, presumed to have been made in Britain, and three-arm rings / ankle-rings presumed to have been made in West Africa.
Evidence suggests that two of the manillas were made by the Harford and Bristol Brass Company in the late 18th Century. The third manilla is from the from the wreck of the schooner Duoro, lost off the Scilly Isles in 1843, and presumed to have been made in Birmingham.
The two arm-rings and an ankle-ring are stylistically different to the manillas and are presumed to have been made in West Africa by recycling manillas or brass hollow-ware. Evidence, however, links the rings to the Harford manillas; hence are assumed to be of similar date.
In 2021, an opportunity arose to conduct a metallurgical analysis of the artefacts by the Deutsches Bergbau-Museum Bochum. The analysis not only determined the composition of the material from which the artefacts were made but also included a comparison with a lead isotope tracing database. The artefacts each contain a small proportion of lead which by use of the database enables their source to be identified.
This short paper at the link summarizes the background to the Saltford artefacts and the preliminary results of the metallurgical analysis.