 The delay usually lasts just before this apex, at an optimum velocity, where a small explosion shoots the firework's stars in desired directions and thus producing a brilliant effect.The colors, reports, flashes, and, stars are analogous to flavor one adds with spices (chemicals with special pyrotechnic properties) to a soup of otherwise bland gunpowder.Gunpowder's relatively low specific impulse (amount of thrust per unit propellant) limits its capacity of thrust production on larger scales.