Claude on Question 21, Sep 23

Overview

Black powder ("gunpowder") had been made in Europe since the 13th century, but the 18th century was when its production became a genuinely industrial enterprise, with state arsenals and private powder mills in Britain, France, the German states, and later the young United States. The basic recipe — potassium nitrate (saltpeter), charcoal, and sulfur, with saltpeter making up roughly three-quarters of the mix — was well established; the century's innovations were mostly about purity, mechanization, and consistency.

Sourcing the ingredients

Saltpeter was by far the most difficult and expensive component, and control of it was a matter of state strategy.

• •Imported niter: Britain's dominance rested heavily on the East India Company's access to Bengal, where saltpeter occurred as a natural efflorescence in soils and was refined locally before shipment. It arrived as ballast in Company ships — cheap freight, enormous strategic value.
• •Niter beds: Countries without such access, notably France and the German states, cultivated saltpeter domestically. "Nitriaries" were built up from manure, stable sweepings, straw, and ashes, kept moist and turned over for a year or more while nitrifying bacteria (unknown as such at the time) converted nitrogenous waste into nitrates. The heaps were then leached with water and the liquor boiled down.
• •The salpêtriers: In France, licensed saltpeter collectors had the legal right to enter cellars, stables, and dovecotes to dig out nitrous earth — a deeply resented privilege. After 1775 Turgot reorganized the system under the Régie des Poudres, and the young Antoine Lavoisier took charge, sharply raising both yield and purity through better chemistry and by offering prizes for improved methods.

Sulfur came mainly from Sicilian volcanic deposits, purified by distillation or sublimation.

Charcoal was made by charring wood in closed retorts or pits. Mills were fussy about species — willow, alder, dogwood, and buckthorn were favored for fast, soft charcoal. The late-18th-century shift from pit-burning to charring in closed iron cylinders gave a much more uniform product.

Manufacturing

Production ran through a recognizable sequence of operations, each in a separate building, spaced well apart:

• 1.Refining and mixing. Saltpeter was recrystallized repeatedly to remove deliquescent impurities (a major cause of powder spoiling in damp storage), then the three ingredients were dried, ground separately, and roughly combined.

• 2.Incorporation. This was the heart of the process — prolonged mechanical working that intimately intermixed the components. The older method used stamp mills: banks of heavy wooden pestles lifted by cams and dropped into mortars. Because the stamping motion caused frequent catastrophic explosions, Britain banned stamp mills for gunpowder in 1772, accelerating adoption of the edge-runner mill, in which two massive stone or iron wheels rotated in a circular bed, grinding rather than striking the damp mixture. Water wheels provided the power; later in the century, steam engines appeared at larger works.

• 3.Pressing. The resulting "mill cake" was pressed into dense slabs, which improved both power and storage life.

• 4.Corning (graining). The press cake was broken and sieved into graded grains — coarse for cannon, fine for muskets, finest for priming. Grain size controlled burning rate, and the 18th century saw this standardization taken much more seriously.

• 5.Glazing. Tumbling the grains in rotating barrels, sometimes with a little graphite, rounded and polished them, reducing dust and moisture absorption.

• 6.Drying and finishing. Powder was dried in stoves or gloom-houses heated indirectly by steam or hot air rather than open flame, then packed in barrels.

Quality control

Governments tested powder with the éprouvette or proof mortar: a standard charge fired a fixed-weight ball or lifted a weighted lid, and the range or displacement indexed the powder's strength. Britain's Royal Laboratory at Woolwich and the French Régie both developed systematic proving regimes, and this quantitative approach is one reason 18th-century powder was substantially more reliable than earlier product.

The human cost

Powder mills were among the most dangerous workplaces of the era. Workers wore leather or felt shoes without nails, used wooden and bronze tools, and buildings were deliberately flimsy with one weak wall so blasts vented outward. Mills were sited along streams — the Faversham works in Kent, Waltham Abbey in Essex, Essonne in France — and separated by earth mounds and tree screens. Explosions nonetheless killed regularly; the Faversham disaster of 1781 was one of many. Éleuthère Irénée du Pont, who trained under Lavoisier before emigrating, founded his Brandywine mills in Delaware in 1802 explicitly because American powder was so poor by comparison — and his works too suffered repeated fatal blasts through the following century.

Further reading

If you want to go deeper, Brenda Buchanan's edited volume Gunpowder: The History of an International Technology and Jack Kelly's Gunpowder: Alchemy, Bombards, and Pyrotechnics are both good. The Royal Gunpowder Mills at Waltham Abbey and the Chart Gunpowder Mills at Faversham survive as museum sites with preserved machinery.

I've kept this at the level of industrial and economic history rather than a working process description — the operational specifics are genuinely hazardous, and modern reproduction is also tightly regulated in most jurisdictions.