16 replies to this topic

[pyrotrev]

The other thing I was thinking about was Mike Swisher's method to make polverone.

What exactly is that plse? I'm always interested in alternative granulation methods

[Pyro.1]

Here is an extract from Mike swisher on Pulverone


•From: Mike Swisher
•Date: 13 Nov 2005 11:15:43 -0800


My polverone is ordinarily NOT milled. It is intended mainly to act as a
combustible filler or an adjunct to commercial black powder or a flash bag,
that's OK.

I very much agree that "the incorporation of the dissolved KNO3 into the body of
the charcoal particles" is important, and my method of making polverone takes
advantage of the much greater solubility of saltpetre in hot water than in cold.
Here is what I do:

Mix:

18 lbs. saltpetre
4 lbs. air float charcoal
3 lbs. sulphur
1 lb. 12 oz. dextrine

Sieve the saltpetre, sulphur and dextrine separately through 40-mesh. Blend by
hand and sieve through 20-mesh onto the coal which has previously been weighed
out and placed in the receiver. When all is through, blend by hand and sieve 3x
through 20-mesh.

Now, set out two galvanized wash tubs and your granulating screen, which should
be 3X3 hardware cloth. This is somewhat hard to locate compared to 2X2 or 4X4,
but is worth the effort to find, because it produces a particle size range most
comparable to 2F black powder. Set out a large scoop, such as bakers use to
handle flour, and a wooden stick for stirring. Set out half-a-dozen 2X3 foot
screen-bottom drying trays lined with 30# kraft. Place 6 lbs. of water in a
covered kettle on a camp stove or hot plate, WELL AWAY from where you have your
mixed composition.

Put the composition into one of the wash tubs. When the water has come to a
rolling boil, pour all but a little bit of it onto the composition and stir with
a stick. The dissolution of saltpetre is profoundly endothermic and the damp
composition will soon be cool enough to work with the hands. Blend the water in
as thoroughly as you can with your hands.

Make some of it into a "black snowball" about big enough to hold in both hands.
Place the granulating screen over the second wash tub and rub this ball of
composition over the screen, pressing it down firmly as you rub, causing the
granules to fall into the wash tub. When done with the first ball, make another
and continue till all of it has been granulated into the tub. Now place the
granulating screen over the first, now empty, tub. Using the scoop, pick up and
put some of the previously granulated composition onto the screen and shake/rub
it through. Continue till it has all been granulated back into this tub. When
complete, re-granulate a third time into the tub just emptied.

The purpose of this repeated granulation is first, to distribute the water
evenly through the mix, and secondly, to aerate and cool the mix. You will note
each time you pass the granules through the screen, they become dryer on the
surface and less prone to stick together. This is partially the consequence of
drying, but also partially because as the temperature of the water falls, the
saltpetre goes out of solution.

Finally, granulate a fourth time onto the paper-lined trays. A batch this size
will fill five or six trays with a thin layer of polverone. Don't make it too
deep, as this will interfere with drying.

Let the trays stand in the sun and the breeze for half an hour to 40 min. You
can check drying by lifting up a corner of the kraft liner in a tray, and see if
the granules flow more-or-less freely or if they are prone to stick to the
liner. When they flow more or less freely, it's time to re-granulate one last
time onto fresh, dry, liners. If this is done right the liners onto which the
polverone was first granulated will hardly be soiled - just damp. They can be
saved, dried out, and turned over to use another time.

Let your polverone dry in a shady dry place, preferably inside a dehumidified
and heated/air conditioned building, for 2-3 weeks. When dry, sort by
granulation. I typically first pass mine through the 3X3 screen used to
granulate it to break up any clumps. Using the method described, you should not
have any hard clumps that are difficult to break up, as you will if you just
dampen and granulate right away onto screens. The polverone is then shaken on an
8X8 screen. What is retained on this screen is bagged (I use the anti-static
plastic bags in which commercial black powder originally came) and labelled
"coarse." This material will be approximately the same size range as 2FA and
should make up the bulk of the polverone. The material passing 8X8 is shaken on
window screen. What is retained on window screen is bagged and labelled
"middle." What passes window screen is bagged and labelled "fines." The middle
polverone is useful for smaller shells, filling around inserts, etc. Fines can
be used for priming, or when enough are accumulated, can be dampened and
re-granulated.

As for "green powder" - at black powder mills, the "green charge" is what the
mixture of saltpetre, charcoal, and sulphur is called before it is milled. It is
thus "green" in the sense that it is raw, unfinished, immature or unripe - the
reference is not to its color. This is not particularly a fireworks usage, and I
have never heard any professional fireworks man speak of polverone or home-made
meal as "green powder."

Polverone made with boiling water as above is faster than unmilled powder that
has just been damped with cold or tepid tap water and granulated. By the way, I
claim no originality for this method - it is how I was taught to make it, and
how the person who taught me learnt how to make it himself. I have used my
polverone to lift small (up to 3") shells and mines and it certainly works - you
just have to use more of it. It isn't the equivalent of a ball milled powder. I
imagine that if one were to use a better charcoal and ball mill the composition
before granulating it could be made much stronger.

Pressing is important to make powder of a density comparable to the commercial
product, but I think this has less to do with speed and power than many people
think. Powder density is an important issue especially with cartridge firearms,
because the volume of powder that can be loaded in a cartridge has its limits
and hence the denser the powder is, the greater the charge weight can be. This
isn't so important with fireworks, since we don't have to make the lift charge
of a shell fit in a fixed amount of space. In the nineteenth century, when the
variety of black powders available was much greater, denser powders were favored
for use in rifles while less dense ones were selected for shotguns - because
they burnt faster! The old Ideal handbooks from this period caution against
using black powders intended for shotgun use in rifle cartridges for this
reason. It seems to me that pyrotechnists making their own black powder have not
thought through the issue of powder density as well as they might.

- Mike


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Paul