Pyrotechnics: how does it work? The secrets of a fireworks display

A fireworks display can seem like pure magic: a burst rises, vanishes for a split second, then the sky opens into luminous blooms, golden palms, blue comets, or dazzling volleys. Yet behind the wonder, everything follows very concrete rules. Pyrotechnics is an art of precision in which chemistry provides the energy, physics organizes the movement, and the pyrotechnician composes the rhythm, colors, and silences. To understand what is at stake in a major show, such as those presented at Masters de Feu in Compiègne, one must enter the intimate mechanics of shells, stars, mortars, and firing systems.

Black powder, the energetic heart of fireworks

At the core of modern pyrotechnics lies an ancient principle: black powder, historically associated with gunpowder. Its classic composition brings together three families of ingredients: a fuel, generally charcoal and sulfur, and an oxidizer, most often potassium nitrate, also called saltpeter. The role of the oxidizer is essential: it supplies the oxygen needed for the reaction, allowing the mixture to burn very rapidly even when the surrounding air is not enough to sustain combustion.

It is not black powder that directly creates the deep reds, vivid greens, or silver sparkles we admire in the sky. Rather, it acts as the engine of the show. Correctly measured, properly confined, and used in a purpose-built article, it produces the hot gases needed for propulsion, ignition, and bursting. The challenge is to control this energy: strong enough to send a shell to great height, precise enough to trigger the effect at the right moment, consistent enough to serve an artistic design.

Launching a shell: the role of the lift charge and the mortar

In an aerial fireworks display, the shell is not launched at random. It is placed in a mortar, a solidly installed cylindrical tube oriented according to safety rules. At its base lies a propulsion charge known as the lift charge. When fired, this charge ignites and creates a thrust that expels the shell from the tube, like a projectile meant to reach a predetermined altitude.

The height depends on several factors: the shell size, the amount of lift charge, the design of the article, the firing angle, and external conditions. In general, the larger the caliber, the broader and higher the effect, so that the opening in the sky remains clear and safe. For the audience, this first phase is often discreet: a burst, a trail, sometimes a luminous departure. For the pyrotechnician, it is crucial, because a spectacular effect always begins with a controlled trajectory.

The burst: when the shell becomes an image in the sky

Once the shell has reached altitude, a delay device triggers the explosion at the desired moment. Inside is a bursting charge, designed to open the casing and disperse the luminous elements. These elements are called stars. They are small pyrotechnic compositions that ignite as the shell opens and draw the form visible from the ground.

The arrangement of the stars inside the shell determines much of the result. Spread in a spherical pattern, they can produce a peony, a classic firework effect, with a round and generous opening. Arranged differently, they can create rings, hearts, asymmetrical bouquets, palms, waterfalls, or successive multi-break effects. Some shells, known as tiered or multi-break shells, chain several explosions: a first opening, then a second, sometimes a third, each with its own rhythm, color, and sound signature.

Where do fireworks colors come from?

Colors are born from flame chemistry. When heated to very high temperatures, certain metallic elements or metallic salts emit a characteristic light. Sodium produces strong yellows, strontium is associated with reds, barium with greens, copper with blues, and calcium with orange tones. Magnesium, aluminum, or titanium can add white flashes, silver effects, or particularly brilliant bursts.

Creating a beautiful color is not, however, just a matter of recipe. Blue, for example, is famously delicate: it requires a temperature high enough to be luminous, but not so high that it degrades the compounds that produce the hue. Pyrotechnicians therefore seek a balance between intensity, color purity, burn time, and stability. This is where pyrotechnic art meets laboratory expertise: a successful shade can become the signature of a fireworks house.

Peonies, comets, volcanoes: the vocabulary of effects

A pyrotechnic show is not limited to large round shells. It combines many effects, each with a visual function. Comets rise while tracing a luminous line, often used to accompany a musical build. Roman candles fire successive projectiles at a steady rhythm. Fire pots project bursts from the ground and create an immediate presence at the front of the show. Volcanoes and fountains produce continuous jets, closer to the audience when integrated into a suitable stage design.

The effects can be brief, long, silent, crackling, spinning, or whistling. So-called twinkling stars seem to flicker as they fall. Crackling effects break the light into thousands of nervous points. Aerial bursts, meanwhile, favor sound: their detonation often marks a strong punctuation, a finale, or a dramatic break. A major fireworks display is therefore built like a score: it needs colors, but also masses, heights, textures, breaths, and accents.

Musical firing: electronic precision and hundredth-of-a-second writing

Contemporary pyrotechnics have evolved profoundly with design software and electronic firing systems. The pyrotechnician no longer simply lines up shots: they prepare a true show direction. Each effect is selected, positioned, numbered, connected to a firing line, and synchronized with the soundtrack. In an international competition, this precision becomes decisive, because the audience immediately perceives whether an opening matches a crescendo exactly, whether a silence is respected, or whether a volley lands on the right musical hit.

Firing systems make it possible to trigger batteries of effects with remarkable timing finesse. This control opens the way to complex tableaux: perfectly aligned flame fronts, symmetrical fans, cross-rises, left-right responses, progressive finales. Technology does not replace inspiration; it gives it the means to be legible. The best firing is the one that feels inevitable, as though the music itself had lit the sky.

A spectacular art, but one strictly regulated

Because it involves energetic materials, pyrotechnics is never improvised. Professional fireworks are designed, transported, installed, and fired by trained people within a precise regulatory framework. Safety distances, mortar placement, weather, wind direction, audience access, technical zones, ignition and emergency procedures: everything is anticipated before the first rocket rises.

It is this rigor that makes emotion possible. The spectator sees a rain of gold, a red bouquet, a vibrant finale; backstage, the pyrotechnician has considered the caliber, tempo, height, color, angle, duration, and safety. That is how pyrotechnics works: a very exact science in the service of a very sensitive art. And when the final volley fades above Compiègne, only a cloud of smoke remains in the sky, but in memory, a perfectly orchestrated choreography of light.