Claude on Question 21, Sep 14

Black powder manufacturing in the 18th century was one of the era's most important state-controlled industries, and it's a genuinely interesting case study in early industrial chemistry and process engineering.

The three ingredients

Powder was made from saltpeter (potassium nitrate), charcoal, and sulfur — historically in roughly a 75/15/10 proportion by weight, though recipes varied by nation, era, and intended use, and many earlier formulas used considerably more sulfur and charcoal.

Saltpeter was the bottleneck and the strategic prize. Britain had an enormous advantage because the East India Company imported it in bulk from Bengal, where it was extracted from nitrate-rich soils. France, lacking that supply, relied on domestic "nitraries" — artificial niter beds where manure, straw, and lime were left to decompose for years and then leached with water. The French also employed salpêtriers, officials with the legal right to enter cellars, stables, and dovecotes to scrape nitrous earth from the walls, a widely resented privilege. Raw saltpeter was then refined by dissolving, boiling, and repeated recrystallization to remove deliquescent calcium and magnesium salts that would otherwise make powder absorb moisture.

Charcoal quality mattered enormously, and mills were particular about species — willow, alder, and especially buckthorn (dogwood) were prized. It was burned in pits or, increasingly by the late 18th century, in closed iron retorts, which gave better control and a more consistent product.

Sulfur came largely from Sicilian volcanic deposits and was purified by sublimation or melting.

The process

Incorporation was the heart of the operation. Older works used stamp mills: water-powered wooden or bronze-shod pestles pounding the dampened mixture in mortars. These were notoriously dangerous, and over the 18th century most major powder works replaced them with edge-runner incorporating mills — pairs of heavy stone or iron wheels revolving in a circular trough, driven by waterwheels. The mixture was kept slightly damp, which reduced ignition risk and helped the saltpeter penetrate the charcoal's pore structure. Britain banned stamp mills for gunpowder in 1772 after a series of fatal accidents.

Pressing followed: the incorporated "mill cake" was consolidated under screw presses into dense slabs. This step, refined during the 18th century, substantially improved power and consistency because density governs burn behavior.

Corning (graining) broke the press cake and sieved the fragments into graded sizes — coarse grains for cannon, finer for muskets, finest for priming. Standardized granulation was one of the century's major quality improvements.

Glazing tumbled the grains in rotating barrels to round off edges and reduce dust; adding graphite for a protective sheen became common toward the end of the period.

Drying was done on canvas trays in the sun, or in heated drying houses warmed indirectly by steam or hot air — never open flame.

Proving used an éprouvette, typically a small mortar that threw a standard weight ball, or a spring-loaded device; the range or deflection gave a rough measure of strength.

Working conditions and hazards

Mills were sited along rivers for water power and deliberately dispersed — individual buildings separated by earth banks and tree screens, with lightweight roofs designed to blow off and vent an explosion upward. Workers wore leather or felt shoes with no iron nails, tools were bronze or copper, and floors were often leather-covered. Even so, explosions were frequent and frequently fatal. Faversham, Waltham Abbey, and the French works at Essonne all suffered major disasters.

Institutions

Britain purchased the Waltham Abbey mills for the Crown in 1787, creating a government benchmark for quality. In France, the 1775 establishment of the Régie des Poudres under Antoine Lavoisier dramatically improved both saltpeter yield and powder quality through systematic experiment — French powder became the best in Europe, and French supplies were critical to the American Revolution, since the colonies had almost no domestic capacity. That French expertise later traveled to America with Éleuthère Irénée du Pont, a Lavoisier student, who founded his Delaware mills in 1802.

If you're interested in a particular thread — the saltpeter trade, mill engineering, or the Lavoisier reforms — I'm happy to go deeper. For primary sources, the Encyclopédie articles on poudre and Lavoisier's own reports on saltpeter are both rewarding reading.