Gemini on Question 21, Sep 20

The manufacturing of black powder (gunpowder) in the 18th century was a massive, highly dangerous, and vital industry. During this time, production transitioned from small-scale artisanal workshops to large, organized mill complexes driven by water or animal power.

The standard recipe had largely stabilized by this era: 75% saltpeter (potassium nitrate), 15% charcoal, and 10% sulfur.

Here is a step-by-step breakdown of how black powder was manufactured in the 1700s.

1. Sourcing and Purifying the Ingredients

The quality of black powder depended entirely on the purity of its three ingredients.

• •Saltpeter: This was the most difficult and expensive ingredient to obtain. It was harvested from "niter beds"—compost piles of manure, decaying vegetation, earth, and human or animal urine, which were left to rot for months or years. The earth was then collected, mixed with wood ash, and flushed with water (leaching). The resulting liquid was boiled in large copper vats until the water evaporated, leaving behind saltpeter crystals. In the late 18th century, the French chemist Antoine Lavoisier revolutionized this process, vastly improving French gunpowder.
• •Charcoal: Hardwoods were useless for gunpowder; they burned too slowly. Manufacturers used softwoods like willow, alder, or dogwood. The wood was stripped of bark and slowly baked in brick kilns or iron retorts to carbonize it without turning it to ash.
• •Sulfur: Most sulfur in the 18th century was imported from volcanic regions, primarily Sicily. It arrived in crude blocks and was purified through sublimation—melting and boiling it in iron pots so the pure sulfur vapor would rise, condense, and be collected, leaving impurities behind.

2. Milling and Incorporation

Simply mixing the three dry ingredients together creates a very poor explosive. The ingredients had to be crushed and forced into intimate contact with one another at a microscopic level. This was called "incorporation."

• •The Edge-Runner Mill: In the 18th century, water-powered edge-runner mills became the industry standard. These featured two massive, heavy stone wheels (often weighing tons) that rolled in a circle over a stone or wooden bed containing the ingredients.
• •Wetting the Powder: To prevent the friction of the stones from igniting the powder, and to help the ingredients bind, the mixture was kept constantly damp. Workers added water, or sometimes stale urine or spirits, creating a thick, black paste known as "mill cake."

3. Pressing and Corning

Earlier forms of gunpowder (called "serpentine powder") were fine dust. Dust was problematic because the heavy sulfur and saltpeter would sink to the bottom of a barrel during transport, ruining the mixture. It also absorbed moisture easily and burned inconsistently. The 18th-century solution was corning.

• •Pressing: The damp mill cake was layered between copper plates and put into a massive screw press. It was squeezed under immense pressure to squeeze out excess moisture and create a dense, hard slate of gunpowder.
• •Corning (Granulation): These hard slates were broken up with wooden mallets. The broken pieces were then forced through sieves made of parchment or brass wire. This broke the powder into specific, uniform grain sizes.
• •Sorting: Different weapons required different grain sizes. Large grains burned slower and were used for cannons; medium grains were used for muskets; and very fine grains were used for pistols and priming pans.

4. Glazing

The freshly corned grains were rough and could easily rub against each other, breaking down into dust again. To fix this, the grains were placed into large wooden barrels and tumbled for several hours.

The friction of the tumbling rounded off the edges of the grains. Often, a small amount of graphite was added to the barrels. This gave the grains a shiny, slippery, black coating (hence "black powder") that made the powder highly resistant to moisture and prevented the grains from breaking apart during transport in horse-drawn wagons or ships.

5. Drying

The glazed powder still contained moisture from the milling process. It was dried either by being spread out on canvas sheets in the sun (which was weather-dependent) or placed in specially designed "gloom stoves." These were drying houses heated by copper pipes carrying steam or indirect heat from a furnace located on the outside of the building, preventing any open flames from getting near the powder.

6. Testing (Proving)

Before being sold to the military or civilians, the powder was "proved." Inspectors used a device called an eprouvette (powder tester). A standard amount of powder was placed in a small chamber and ignited. The explosion would push against a weighted lever or a ratcheted wheel. If the wheel turned a specific number of clicks, the powder was deemed strong enough for military use.

Safety Measures in 18th-Century Mills

Gunpowder mills blew up with alarming frequency. To mitigate this, 18th-century manufacturers implemented strict safety protocols:

• •No Iron: Workers could not use iron tools, which might strike a spark. Tools were made of wood, copper, or bronze.
• •Footwear: Workers had to wear leather slip-ons, felt shoes, or work barefoot. Iron shoe nails were strictly forbidden.
• •Mill Layout: Mill buildings were built flimsy, often with three strong stone walls and a fragile wooden roof and front wall facing a river. If an explosion happened, the blast force was directed outward and upward, rather than destroying the heavy machinery. Buildings were also spaced far apart and separated by blast walls or thick lines of trees.