Home Manufacture of Black
Powder

Without black
powder in all its varieties, it would be tough to make much more than
sparklers for pyrotechnical displays. Making high performing black powder
is one of the fundamental skills that the aspiring pyrotechnician will
probably want to master early in his quest for knowledge in the field. The
goal of this meager treatise is to illustrate the most popular method of
amateur production which is called the "ball milling method." This implies
that anyone who wants to use this approach will need to first build or
have access to an efficient ball mill
. Without a mill, one is left with the inferior alternatives of using
the CIA (precipitation) method or the incredibly laborious mortar and
pestle method.

The first step in
the process is to assemble the raw materials. In this case, there are only
three, as pictured: potassium nitrate, charcoal and sulfur. Of these
three, potassium nitrate and sulfur can readily be purchased from pyro
supply companies such as Skylighter
or Iowa Pyro Supply ,but
charcoal is a different story. The subject of charcoal could require a
whole book to adequately cover. For the purpose of brevity, this text will
assume that willow charcoal is one of the most popular choices for making
high performance black powder. Unfortunately, commercial sources (at least
in the US) for this particular kind of charcoal are very rare. The best
approach is to make it yourself with a home-made
charcoal cooker. Then you can control some of the characteristics of
your charcoal by custom cooking it to your liking. .

If you make your
own charcoal, you need to reduce it from the original sticks to a more
usable powder form. I use the meat grinder method shown here. A guide
chute has been fashioned from a sheet of transparency film to help keep
the dust down. This is definitely not a job to do in your kitchen unless
you want to risk sleeping in the garage for a month. A good respirator is
also recommended. The result is a charcoal powder which ranges from air
float to about -8 mesh. This may or may not be useful "as is" for making
black powder, depending upon the approach used to make the green meal.
Hopefully, this will become clear in a moment.

Regardless of the
method used to make the green meal, the proper proportions can only be
achieved by weighing them on a scale. I generally use the traditional
ratio of 75 parts potassium nitrate, 15 parts charcoal and 10 parts
sulfur. If your black powder is intended primarily for use as lift powder,
you might want to use the ratio which is purported to be optimized for
this purpose. It is 74 parts potassium nitrate, 14 parts charcoal and 12
parts sulfur. Just remember that these are parts by weight. It seems that
every "newbie" to pyrotechnics will reveal his ignorance by asking the
question concerning whether parts in a formula refers to weight or volume.
Save yourself the embarrassment and etch upon your mind that pyro formulas
are always in parts by weight unless specifically stated otherwise. The
triple-beam balance scale shown does the trick quite nicely for weighing
out parts of a formulation, but you can accomplish the same purpose with a
much less expensive home-made
scale .

Let's diverge to a little
background discussion for a minute. The green meal referenced above is the
raw, unprocessed mixture of the constituent ingredients. There are two
basic approaches to creating this initial mixture. One method is to create
a bulk mixture from which a "volume measured" portion is taken and placed
in the milling jar. The other approach is to create a batch of green mix
which is exactly the amount needed for the intended milling jar charge. In
the first case, the particle size of the individual components of the mix
must be small enough to assure homogeneity. In the second case, there is
no concern about the green meal being homogeneous. The potassium nitrate
and sulfur can be full of lumps and the charcoal can be very coarse. The
proper weight portions are just loaded into the mill jar and the milling
accomplishes the homogeneity. The second approach has many advantages, but
it can only be done if the user knows the exact weight of the optimum
charge for his milling jar. For the purposes of this discussion, the
definition of an optimum charge is the following: the amount of fully
milled black powder meal which occupies 25% of the mill jar volume. The
determination of this optimum charge is challenging because milling will
often alter the volume of that which is milled. The best way to determine
the weight of the optimum charge is to actually weigh the desired volume
of finished meal. This implies that the user of a new
milling jar must use the first approach to making green meal for his
first batch. The optimum charge is then determined and can be used for all
succeeding batches.

The first approach
to making green meal will be demonstrated because it also includes many
principles of properly mixing pyrotechnic chemicals. In general,
successful pyrotechnic compositions work well because their proportions of
ingredients have been very carefully determined. If the pyrotechnician
allows the proportions of his mixture to vary from the ideal, the
performance of the composition will usually suffer. Therefore, except in a
few unusual cases, a high degree of homogeneity is desired in pyrotechnic
mixes. One of the best ways to accomplish this is by using screening
(which requires a good set of mixing
screens ) as a means of mixing pyro chemicals together. In the picture
at the left, is shown the results of screening a mixture of the potassium
nitrate and sulfur which were weighed out for the bulk black powder green
mix. The two chemicals were stirred together and appeared well mixed.
However, upon passing the mixture through a 40 mesh screen, many large
lumps of sulfur are revealed. These lumps obviously destroy the
homogeneity of the mix in their near vicinity.

In order to
eliminate these lumps, I perform a rough approximation to a mortar and
pestle operation by placing the lumps in a container. The lumps are
crushed by the back of a spoon against the sides of the container. The
contents of the container are then returned to the mixing screen box and
the cycle is repeated until all of the material passes through the screen.
The entire quantity of mix is then passed through the screen several more
times to ensure a thorough mixture. This method works well if the lumps
aren't hard and dense. If they are too hard to crush easily, the best way
to eliminate them is by milling each chemical separately prior to mixing
with others. Now, to complete the black powder green mix, the charcoal
must be added. The screening method could have been used to mix all three
chemicals together in one step, but I prefer to add the charcoal as an
"airfloat" which will be free of coarse particles. The charcoal is added
to a container with the screened potassium nitrate and sulfur, a tight lid
is used to close the container and the container is shaken vigorously. I
do this because screening any mix which contains fine charcoal will
usually result in a lot of airborne dust which enters the lungs and coats
the pyro lab with a nasty black film. At this point, a black powder green
meal with a reasonable degree of homogeneity has been achieved.

Now a volume of
green meal equal to 25% of the mill jar volume is measured. For this jar,
that volume is 3 and 1/4 cups of our bulk green meal. This is the first
approximation to the theoretically ideal mill jar charge. It is added to
the jar along with hardened lead milling media equal to 1/2 of the mill
jar volume. In my experience, the volume of the black powder meal will
increase during the milling. If you have a high efficiency mill, the
milling process will be complete in about 3 hours of milling time. I would
be remiss if I didn't mention that the milling should be done with all the
due precautions taken. This means locating the mill remotely and perhaps
using protective barriers around it.

The powder which
results from the milling process is still referred to as "meal" because it
is not yet very useful for pyrotechnic applications. However, it is no
longer called green meal. The meal is processed into grains of black
powder by a method known as corning. The size and characteristics of these
grains will determine some of the aspects of the performance of the
finished black powder. The first step in the corning procedure is
accomplished by using a powder
die to compress the milled powder into "press cake". One of the
secrets of making durable black powder grains is to add sufficient
moisture to the meal prior to pressing it into the cake. I add 4 grams of
50% water/50% alcohol to 119 grams of milled meal to make an individual
die batch. This is done by placing the meal and water/alcohol in a mixing
cup and stirring vigorously with a stirring rod. The milled powder will
undergo a fairly rapid transition from fluffy, loose powder to a stiff,
but still crumbly powder when the moisture becomes well distributed. Some
will advocate adding moisture by misting it lightly onto a pile of milled
powder while mixing with the diapering method. Theoretically, this avoids
degrading the performance of the powder by not giving the potassium
nitrate a chance to dissolve and recrystallize. However, I have found this
trouble to be unnecessary. The picture shows the dampened, milled powder
being added to the powder die, after which the compression piston is
placed on top.

Next, the die is
placed in a home-made
hydraulic press and the press is operated from behind the blast
shield. This picture is illustrative of the pressing step, but in actual
operation I recommend the use of a heavy glove on the hand which is used
to pump the hydraulic jack. This and a heavy sleeved shirt or coat are a
good idea. The die has been designed so that the finished press cake has
the desired density of 1.7 grams/cc.

These are the puck
shaped pieces of press cake which are extracted from the powder die after
pressing has been completed. They are rock hard and should hold together
well without crumbling. If the press cake crumbles easily, this is one
indication that insufficient moisture was added to the milled powder. The
press cake pucks are allowed to air dry for at least 24 hours before they
are crushed into powder grains. Tapping on the pucks with a wooden dowel
makes a china-like clinking noise even right from the powder die. After
drying for a day or so, the pucks will ring even a little more, indicating
that the moisture level is about right for the final step of the corning
procedure.

Crushing the press
cake into useful grains is somewhat nerve-wracking for me, but I like this
step because it is the last in a long series required to finally obtain
high performance black powder. I use a small baseball bat to crush about
1/2 of a press cake puck at a time. The chunk of press cake is placed in
an old aluminum pressure cooker pan and the bat is used in short, downward
strokes to break up the cake. This works best if the pan is placed on a
very hard surface, such as concrete or stone. The idea is to fracture the
cake into grains without crushing it back into useless powder. Again, for
safety's sake, this should be done outdoors with protective clothing and
always avoid placing your face directly over the pan. If 60 grams of black
powder were to ignite in the pan, it would create a hot flame as much as 4
feet high before your reaction time would allow you to get out of the way.
As I said, this step is a little nerve-wracking, but I have never had an
accident during this step yet. There may be some arguments for using a
plastic bucket instead of an aluminum pan, but I'll leave this choice open
to discussion.

The contents of
the crushing pan are emptied into a stack of screens to separate the
various desired grain sizes. Whatever will not pass through the top screen
is returned to the pan for more crushing with the "bat pestle" and this
cycle is repeated until all the black powder cake passes through the first
screen. A little side to side shaking of the screen stack during each
cycle helps the grains settle to their proper location in the stack. This
particular stack of screen boxes consists of the catch box, a 40 mesh, a
20 mesh, a 10 mesh and a 4 mesh screen on top. The powder which falls
clear to the catch pan is a -40 mesh powder which is retained for use
whenever meal D is called for in my pyro formulas. The powder in the 40
mesh box is a 20 to 40 mesh powder which is used as 4FA equivalent. The
powder in the 20 mesh box is a 10 to 20 mesh powder which is used as 3FA
equivalent. Finally, the powder in the 10 mesh box is a 4 to 10 mesh
powder which is used as 2FA equivalent.

This picture is
shown to give an idea of the various grain sizes relative to common US
coins. Now I'd like to explain a little about my philosophy regarding my
choice of screens for separating the grains into these ranges. The ranges
don't conform exactly to those given for the common commercially produced
powders and this is intentional. The only motivation I can think of to
conform more closely with the commercial definitions for black powders is
to enable a completely transparent exchange of commercial and home-made
powders in pyrotechnic projects. In these cases, the pyro craftsman wants
his home-manufactured powders to perform identically to commercial powders
so that he can always expect consistent end results. In my case, I don't
use commercial powders. Therefore, I can afford the luxury of adjusting
the amounts of powders used in my projects according to the desired
results. This way, my only concern is to make my own manufacturing process
very consistent so that my home-made powders always give me the same
results. The advantage of this approach is that the ranges of grain sizes
for my equivalent powders don't overlap as they do in the commercial
ranges. This means that I can use commonly available screens and do
multiple separations in one step as illustrated above.

Finally, I am compelled to
add a few words of caution and disclaimer to this brief explanation.
Remember that the manufacture of black powders is a regulated activity in
many areas. One should do some research into the legal requirements before
attempting to do any of these steps. The procedures described represent my
own experience and are not necessarily recommended as the final word in
how to do it properly and safely. These explanations are made available to
others in order to stimulate constructive dialog for enhancement or
improvement.

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