It is generally recognized that fireworks originated in China during the Sung dynasty (960-1279). A cook in ancient China discovered that a mixture of sulphur, saltpetre, and charcoal was highly flammable and would explode if confined in a small space. This discovery was first used for entertainment. The technique was soon adapted to weaponry and used to shoot rocket-powered arrows. In the 7th century the knowledge spread west via Arabia, reaching Europe in the 13th century where pyrotechnics developed with the invention of the gun in the 14th century. It was not until the 19th century that fireworks became as vividly colourful as we know them today. Brilliant colours are achieved by combining potassium chlorate and various metallic salts. These salts produce a variety of colours: strontium burns red; copper makes blue; barium glows green; and sodium produces yellow. Magnesium, aluminium and titanium give off white sparkles or a flash. Every firework show is a fantastic display of physics. The pyrotechnist has to take into account the relationships between vectors, velocities, projectiles and their trajectories together with the explosion forces behind burst patterns.