Malachite’s Big Hole
Black Powder Production Through Time:
The earliest forms of gun powder were simply dry mechanical mixtures of the three components, sulfur, charcoal and nitre (saltpeter or potassium nitrate). These dry mechanical mixtures were known as serpentine powder and were extremely dangerous to handle, but when properly mixed produced a very rapid burning powder. Due to differences in specific gravity, the components tended to separate during shipment, and it was often necessary to remix the powder just prior to use to obtain a useable product.
The first major advance in powder manufacture was the addition of water during the mixing process. This greatly reduced the danger of accidental explosion during mixing, and also made the process of corning (granulating) the powder possible. Powders which were corned while wet didn't have the problem of unmixing during transport, resulting in powders which performed more uniformly.
By the 1700's gun powder manufacturing was a major industry in all European nations as well as colonial America. Native sulfur was usually obtained by importation from the vast sulfur deposits of Sicily, however, nitre and charcoal could be obtained locally. Nitre is a leachate from manure, and in 1700's Europe and colonial America the contents of barnyards, outhouses, and bat-cave deposits were considered the property of the government.
At the time of the American Revolution, manure was subject to three leachings, and then the residue was mixed with lye water. The resulting liquor was then boiled to produce crystals of potassium nitrate. Early powder makers were particularly concerned with the purity of the nitre, and the potassium nitrate crystals might be re-dissolved and re-crystallized several additional times, each cycle improving the purity of the component.
Charcoal was produced by burning wood in ovens in which access of fresh oxygen could be closely controlled. Once high temperatures were reached inside the oven, the flow of oxygen (fresh air) could be cut-off resulting in a residuum of nearly pure carbon. For high quality powders, the woods of alder, willow or similar woods were preferred because the soft charcoal they produced was readily ground to a fine particle size. Charcoal production was usually done by the powder manufacturer so that the quality of the charcoal powder could be more closely controlled.
At the time of the American Revolution, the components were mixed and ground in stamp mills, a mechanical equivalent of a mortar and pestle, being driven by water power or by animals. The components were measured out at a ratio of 75% nitre, 15% charcoal and 10% sulfur with enough water added to make a thick paste. These mills were not efficient and required 20-24 hours to produce a good powder.
After milling, the powder was corned by forcing the thick paste through a screen or screens corresponding to the size of grains desired. This resulted in a rough or "unglazed" powder. If the powder was to be glazed, the still damp grains were placed in a rotating drum which rounded off the rough edges and polished or "glazed" the powder. Another sifting of the powder was required to separate the grains of the desired size from the fragments and dust resulting from the glazing process. The residue was returned to the stamp mill to supplement the feedstock.
The final step of the process was to dry the powder. Most mills had a "dry house" where heat could be directed over trays of powder and remove any residual moisture. After the powder was moisture free it could be packed for shipping.
An additional step pressing the powder was added in the 1780's and was common by about 1805. After milling was complete, the moist powder was pressed between to plates. Pressing increased the specific gravity of the powder and removed micro-air pockets in the grains. These slabs of "press-cake" were then run through rollers to break them up and then the particles were run through screens for sizing and drums for glazing as before. Pressing greatly improved the performance of the powders, and the military found it could reduce charge volumes by 20-30 percent while maintaining performance.
The wheel mill (which had been used to mill grains for centuries) was adapted to milling gun powders about the same time as the powder press. Because the wheel mill both rolls and rotates, it adds a considerable "scuffing" motion to the component mixture as it is being ground. Wheel mills were far more efficient than stamp mills and could produce a top grade powder in four to eight hours.
In the late 1800's graphite (black lead) was added to the glazing barrels. The graphite both improved the polish and helped repel moisture. The disadvantages were that graphite made the powder more difficult to ignite, slowed its burn rate and made for a dirtier burn. The British Government specified that no "black lead" was to be used in the manufacture of powders to be used for military purposes.
By the 1890's the manufacture of black powder was a perfected science. Through the use of different milling times, granulation sizes, and ingredient mixes, almost any burn rate required for use as a propellant could be produced. As smokeless powders became widely available, the use and quality of black powders declined.
The above article is a summary of The Making of Black Powder, by Dan Phariss printed in the Black Powder Report, March 1985.