Gemini on Question 21, Sep 25

In the 18th century, black powder (gunpowder) was the only explosive and propellant in the world, making it a critical strategic resource for every major power. By this time, the process had evolved from medieval alchemy into a proto-industrial, highly organized—and incredibly dangerous—manufacturing process.

The ideal recipe was generally standardized at roughly 75% saltpeter, 15% charcoal, and 10% sulfur.

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

1. Sourcing the Ingredients

Obtaining the raw materials was often the most difficult part of the process, particularly for the main ingredient.

• •Saltpeter (Potassium Nitrate): This was the oxidizer that made the powder burn, and it was notoriously hard to acquire. Nations without access to natural deposits (like those in British-controlled India) had to make it. They created "niter beds"—large heaps of decaying organic matter (manure, straw, and human or animal urine) mixed with limestone. After rotting for over a year, the soil was washed with water to extract calcium nitrate. Wood ash (potash) was added to chemically convert it into potassium nitrate. It was then boiled and cooled to form saltpeter crystals.
• •Charcoal: This provided the fuel. Not just any wood would do; powder makers required lightweight woods like willow, alder, or dogwood. The wood was slowly baked in pits or iron retorts (without oxygen) to turn it into charcoal.
• •Sulfur: Sulfur lowered the ignition temperature of the mixture and increased the speed of combustion. It was typically imported from volcanic regions, with Sicily being the primary supplier for much of Europe.

2. Refining and Prep

Before mixing, the ingredients had to be purified. Saltpeter was boiled and crystallized several times to remove sea salts, which would attract moisture and ruin the powder. The sulfur was melted and skimmed of impurities. All three ingredients were then ground into fine powders individually—a safe process since they were not explosive on their own.

3. Incorporation (The Milling Process)

This was the most crucial and dangerous step. Mixing the ingredients by hand was no longer sufficient for 18th-century warfare; the ingredients had to be mechanically smashed together so deeply that they essentially became a single substance.

• •Stamp Mills: Earlier in the century, heavy wooden pestles (driven by water wheels) would rise and drop into mortars containing the ingredients.
• •Edge-Runner Mills: As the century progressed, powder makers shifted to edge-runner mills. These featured two massive, vertical stone wheels (weighing tons) that rolled in a circular trough over the ingredients.
• •The "Wet" Rule: To prevent the friction of the stones from igniting the powder, workers constantly added small amounts of water, turning the mixture into a thick, black paste known as "mill cake."

4. Pressing

The wet mill cake was scooped out of the trough and layered between copper plates or canvas sheets. It was then put into massive wooden screw-presses. Men would turn the presses to squeeze out excess water and compress the paste into dense, hard, slate-like blocks. Compressing the powder ensured that the ingredients were packed as tightly together as possible.

5. Corning (Granulation)

In its dust form (known as "serpentine" powder), gunpowder burned too fast, fouled gun barrels, and absorbed moisture easily. The 18th-century solution was corning.

• •The pressed blocks of powder were smashed with wooden mallets into smaller chunks.
• •These chunks were forced through wire or parchment sieves to create uniform grains (corns).
• •Different sizes were sorted for different weapons: large grains for cannons (which needed a slightly slower burn to prevent the barrel from exploding), and fine grains for muskets and pistols.

6. Glazing

The jagged grains of powder were poured into large wooden barrels and tumbled for hours. The friction rounded the edges of the grains, preventing them from breaking down into dust during transport. Often, a small amount of graphite was added during this process. The graphite coated the grains, making them highly resistant to moisture and allowing them to pour smoothly down the barrel of a musket.

7. Drying and Packaging

The glazed powder was still slightly damp. It was spread out on wooden trays in special drying houses. Sometimes it was air-dried, but in damp climates (like Britain), it was dried using a "gloom stove"—an iron stove fed from the outside of the building so that no open flame was ever inside the drying room. Finally, the finished powder was packed into wooden barrels for shipping.

Quality Control: The Eprouvette

To test the strength of a batch of powder, 18th-century testers used a device called an eprouvette (powder tester). This looked like a small pistol, but instead of firing a bullet, the explosion pushed against a metal wheel attached to a calibrated spring. Depending on how many notches the wheel turned, the buyer could tell how powerful the powder was.

The Danger and Design of Powder Mills

Gunpowder mills exploded with terrifying regularity. Because they relied on water wheels for power, they were built along rivers, usually isolated from towns.

To mitigate the loss of life and property, 18th-century powder mill buildings were built with a specific architecture: three walls were made of thick, heavy stone, while the roof and the wall facing the river were made of flimsy, lightweight wood. If an explosion occurred, the blast would be directed outward toward the river and upward through the roof, sparing the rest of the facility and neighboring buildings from the shockwave. Workers were forbidden from wearing shoes with iron nails, lest a spark on a stone floor ignite the dust.