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Flash Powder

Background

Flash powder is used in many pyrotechnical, magic, and theatrical
demonstrations; should be used with extreme care and be avoided if the
same effect can be achieved by some other means. It will detonate if confined by
even a few layers of newspaper and is hazardous due to its sensitivity to
friction, static and heat and becomes a lot more sensitive when wet.

Having said that, flash powder is probably one of the most widely used
compositions in the pyrotechnic industry. It is used to produce dazzling visual
effects, loud cracks and bangs, as a bursting charge and as an ignition charge
for other compositions.

Composition

There is a huge number of possible compositions, all of which will produce a
slightly different effect and have different characteristics. Below is just some
of the possibilities. These are here as examples only, you should not carry
these out unless you have accurate information about the safety of each.

Ingredient

Formula

Standard

US Army

Nitrate

Green

potassium perchlorate

KClO4

70%

64%

43%

aluminium powder

Al

30%

20%

aluminium dark flake

Al

22.5%

aluminium dark pyro

36%

sulfur

S

10%

30%

antimony sulfide

Sb2S3

3.5%

potassium nitrate

KNO3

50%

barium nitrate

Ba(NO3)2

21%

As you can see, there is a huge amount of room for variation.

Here is some information on varying the composition of flash powder.

Oxidiser/Fuel Ratios

It is possible to have as much as 75% oxidizer all the way down to 38%.
Basically, the more oxidizer: the faster it will burn and the less light given
off; the more aluminium: the slower it will burn and the more light it will give
off. A good rule of thumb is to have proportions falling within these
specifications: 40-70% oxidizer, 20-40% aluminum, 20-30% sulfur or antimony
trisulfide (if you are going to use it at all).Just to give you an idea of the
variation which is possible, I have seen successful flash powder made from
magnesium filings (that's filings not powder) and potassium permanganate.

Magnesium

It is possible to use magnesium instead of aluminium, however you should take
care when using magnesium as it can cause the composition to spontaneously
explode when stored (you should avoid storing flash powder in the first
place).

Sulfur/Antimony Trisulfide

These two chemicals are added for two reasons:

As an ignition promoter, that is, to lower the ignition temperature of the
composition

To deepen the noise which is made from a crack to a boom. This phenomenon
is not fully understood.

You should not use potassium chlorate (or any chlorates) when using sulfur to
a composition as the sensitivity is increased by up to ten times.

Oxidizers

The most common oxidizers are potassium perchlorate and potassium chlorate.
It is advised that you use the perchlorate rather than the chlorate as it is
much safer, and the noise from a composition containing chlorate is at best only
slightly better than that from a composition containing perchlorate.

Equations

The equation of flash powder will vary greatly depending on the composition.
Basically there will be aluminium oxide, some chlorine dioxide and maybe some
potassium chloride.