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.
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