Flash powder

History

Lycopodium powder is a yellow-tan dust-like powder historically used as a flash powder.^[1] Today, the principal use of the powder is to create flashes or flames that are large and impressive but relatively easy to manage safely in magic acts and for cinema and theatrical special effects.

In more recent times, the development and dissemination of modern flash powder formulations have been influenced by online pyrotechnic communities. One of the most well-known recipes for flash powder, particularly among amateur enthusiasts, was popularized by an anonymous internet user under the moniker "AegisH8". This individual shared detailed information on specific ratios and preparation techniques that became widely adopted in hobbyist circles.

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Mixtures

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Perspective

Normally, flash powder mixtures are compounded to achieve a particular purpose. These mixtures range from extremely fast-burning mixtures designed to produce a maximum audio report, to mixtures designed to burn slowly and provide large amounts of illumination, to mixtures that were formerly used in photography.^{[citation needed]}

Photo-flash powders

For photography, fuel-rich mixtures containing magnesium and nitrates were used. The excess magnesium is volatilized by the reaction and burns in air providing additional light. In addition, the higher concentration of fuel results in a slower burn, providing more of a "poof" and less of a "bang" when ignited. Various formulas from 1917 include: 1 oz (28 g) potassium nitrate to 1 oz (28 g) magnesium, 2 oz (57 g) magnesium to 0.5 oz (14 g) chrome alum, and 2 oz (57 g) magnesium to 0.5 oz (14 g) potassium chlorate.^[2] Fuel rich flash powders are also used in theatrical flash pots.^{[citation needed]}

Magnesium based compositions degrade over long periods, meaning the metallic Mg will slowly react with atmospheric moisture. Commercial photographic flash powders are sold as two-part mixtures, to be combined immediately before use.^{[citation needed]}

Aluminium and chlorate

The combination of aluminium powder and potassium chlorate is unstable, and a poor choice for flash powder that is to be stored for more than a very short period.^{[citation needed]} For that reason, it has been largely replaced by the potassium perchlorate mixtures.

The simplest is a two-component chlorate mix, although this is rarely used.

KClO₃ + 2 Al → Al₂O₃ + KCl

The composition is approximately 70% KClO₃ : 30% Al by weight for the reactants of the above stoichiometrically balanced equation.

Sometimes a few percent of bicarbonate or carbonate buffer is added to the mixture to ensure the absence of acidic impurities.

Sulfur is often added as a third component to this mixture^[3] in order to reduce the activation energy. Antimony trisulfide may be used as an alternative and is more stable in storage.^{[citation needed]}

Potassium nitrate, aluminium and sulfur

This composition, usually in a ratio of 5 parts potassium nitrate, to 3 parts aluminum powder, to 2 parts sulfur,^[4] is especially popular with hobbyists.^[who?] It is not very quick-burning unless exceptionally fine ingredients are used.^{[citation needed]} Adding 2% by weight boric acid can potentially improve shelf-life and help prevent spontaneous combustion, as it neutralises amides created by decomposition of the nitrate.^[5]

2 KNO₃ + 4 Al + S → K₂S + N₂ + 2 Al₂O₃

The composition is approximately 59% KNO₃ : 31.6% Al : 9.4% S by weight for the reactants of the above stoichiometrically balanced equation.

Aluminium and perchlorate

This section does not cite any sources. (June 2025)

Aluminium powder and potassium perchlorate are the only two components of the pyrotechnic industry standard flash powder.

The balanced equation for the reaction is:

3 KClO₄ + 8 Al → 3 KCl + 4 Al₂O₃

The stoichiometric ratio is 34.2% aluminum and 65.8% perchlorate by mass. A ratio of seven parts potassium perchlorate to three parts dark pyro aluminium is the composition used by most pyrotechnicians.^[who?]

Magnesium and nitrate

Another flash composition consists of magnesium powder and potassium nitrate.^[6] Other metal nitrates have been used, including barium and strontium nitrates, which will color the flame during combustion.^[6] This mixture has been applied in solid propellants in aerospace.^[7]

2 KNO₃ + 5 Mg → K₂O + N₂ + 5 MgO

The composition is 62.4% KNO₃ and 37.6% Mg by weight for the reactants of the above stoichiometrically balanced equation.

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Safety and handling

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Perspective

This section does not cite any sources. (June 2025)

Flash powders even within intended usages^[which?] often release deadly amounts of explosive force. Nearly all flash powder mixtures are sensitive to shock, friction and electrostatic discharge. Additionally, accidental contaminants such as strong acids or sulfur compounds can sensitise some of them even more. Because flash powder mixtures are so easy to initiate, there is a high risk of accidental explosion which can inflict severe blast/fragmentation injuries, e.g. blindness, explosive amputation, permanent maiming, or disfigurement. Fatalities have occurred.

Flash powders are often highly sensitive to friction, heat/flame and static electricity. A spark of as little as 0.1–10 millijoules can set off certain mixtures.

Most flash powder formulations (especially those that use micrometre flake aluminium powder or fine magnesium powder as their fuel) can self-confine and explode in relatively small quantities. This makes flash powder dangerous to handle, as it can cause severe hearing damage and amputation injury even when sitting in the open.

Self-confinement occurs when the mass of the pile provides sufficient inertia to allow high pressure to build within it as the mixture reacts. This is referred to as inertial confinement, and it is not to be confused with a detonation.