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Making Black Powder

Making any pyrotechnic composition can be dangerous - nothing is 100% safe.

Ball mills should always be operated in a place where an accident (explosion) will cause minimum damage and no injury - certainly not in your house!

Some people mill BP dampened with alcohol or water - this is still not a guarantee of safety. Make sure you use non-sparking balls & that no grit, metal or extraneous matter has got into your green mix.

Black powder is essential to many firework devices. It is used as the lift and burst medium in shells, in bangers, jumping jacks and many other places.

Although black powder can be bought in some countries, there are often restrictions, shipping difficulties and (because it has few applications) it is now very expensive.

For all these reasons, it is very useful to be able to make your own.

As you will see, this involves far more than just mixing the raw ingredients.

The main stages in making black powder can be summarised as follows:
  • Weigh and mix the raw ingredients (green mix).
  • Mill the ingredients to a fine, incorporated powder (meal powder).
  • Press the meal powder into a solid slab.
  • Break the slabs into grains (corned powder).
  • Sieve the corned powder into different sizes.
The standard modern formula for black powder is:

Potassium Nitrate75
Charcoal15
Sulphur10
n.b. these are parts by weight.

There is endless debate on which is the best charcoal to use, and this is the ingredient that will affect the speed/power of the black powder the most.

A high quality, lumpwood, hardwood barbeque charcoal is a good place to start. As you become more expert, try different types and compare the results.

Weigh the ingredients carefully and place in your ball mill, ensuring that the total charge takes up about 1/4 of the volume of your milling jar. Then add your milling media (which should 1/2 fill an empty milling jar).

Because the Sulphur and Charcoal are much less dense than the Potassium Nitrate the weighed ingredients don't look that much different in volume - trust your scales and not your eyes!

Milling time depends on how effective your milling set-up is and how fine your ingredients are in the first place. I test my powder by the simple expedient of putting about half a teaspoon on the corner of a piece of paper and setting fire to the corner.

As soon as the flame touches the powder, it should burn very quickly, leaving the paper upon which it was resting slightly scorched but intact. If the paper burns along with the powder it is too slow.

There should also be very little residue on the paper - residue indicates poor incorporation.

This picture show the results from a fairly good powder, there is virtually no residue and the paper under the powder is intact. In a very fast powder the paper would only have light brown scorch marks.

This meal powder is very useful as it is for many firework projects, particularly for a formula where gunpowder is mixed with other chemicals.

If you are looking for maximum power however, you will have to granulate it.

When you are satisfied that the meal powder is fast enough, it's time to press it.

n.b. the likelihood of an explosion at this point is quite small, but the consequences would be serious, so you should take all possible precautions.

Most amateurs make black powder by pressing the meal powder in some kind of sleeve. Should the powder explode at this stage bits of the sleeve would fly everywhere with devastating effect. Therefore you should think about what the sleeve is made of and arrange a strong barrier between the press and yourself.

Most commonly, sleeves are made from polyethylene tubing the theory being that this would fragment fairly gracefully compared to PVC which would produce sharp fragments. In industry, the powder was pressed between metal plates and the surplus powder allowed to drop out of the sides. Whatever method is used, a safety barrier is the most important item.

The powder is first damped with a 50/50 mixture of water and alcohol. Powder from the mill is light and fluffy, but damping consolidates it somewhat. The usual ratio is 1ml of water to 100g of powder.

It should not be so damp that water runs from the press, as this would leach out the soluble potassium nitrate and change the ratio of the materials. If it is not damp enough, the pressed puck will crumble.

The sleeve and plunger are then put in the press and the powder pressed - in my case pretty much as hard as I can manage! The press is then allowed to 'dwell' for a couple of minutes.

One theory is that the fine sulphur fills up the gaps and creates a solid cake.

When you take off the pressure and push out the puck, it should be hard and be almost impossible to break with your hands.

The ideal density for a puck is generally taken as 3.6 g/cc. You can check this by weighing the puck and dividing this figure by the volume. The volume of your puck is Pi x radius squared x height.

If your figure is lower than 1.7 g/cc you need to press harder, if it's higher then you have a big press or you are stronger than me!

I like to leave the pucks overnight to dry, but some people proceed to the corning stage straight away.

The idea is to break the pucks into granules, but not to crush them so much that they turn to powder again!

I tend to use a pestle and mortar and hit the pucks rather than grind them.

Don't go too far at first. You can always crush it some more, but it's a lot harder to make it into a puck again!

You then need to put the resulting powder through a stack of sieves to create the various grades you will need.

There are many grades of commercial gunpowder, but for firework use I stick to three sizes.

  • That which passes 4 mesh and is retained on 10 mesh - good for shell lifting charges.
  • That which passes 10 mesh and is retained on 20 mesh - good for Roman Candles, rocket blowing charges etc.
  • That which passes 20 mesh - good for dusting black match.