The first synthetic dye in history was an accident, made by a teenager who was trying to cure a disease. In 1856 an eighteen-year-old chemistry student named William Perkin was attempting to synthesise quinine, the antimalarial drug the world badly needed and could only extract, expensively, from bark. His experiment failed. Instead of medicine he was left with a dark sludge, and when he tried to clean it away he noticed that it stained with an intense and beautiful purple.

Perkin had the wit to see what he was holding. That purple became mauveine, the first commercially produced synthetic dye, and it arrived at a moment when purple still carried the memory of royalty, a colour so hard to make that ordinary people had never worn it. Within a decade the young science of coal-tar chemistry, building on Perkin's stumble, was turning out colours that had once belonged only to kings and making them into things anyone could buy by the yard. A shade that had signalled power became a shade you could put on a Sunday dress.

The consequences ran far past fashion. The dye industry Perkin's accident set in motion grew into the modern chemical industry itself, one of the foundations of the world we live in, all of it descended from a failed attempt at a fever cure. The exhibit puts it neatly: a failed drug turned out to be a colour, and the colour turned out to be an industry. It is a reminder that discovery rarely arrives where you aim it, and that a mess at the bottom of a beaker, looked at by the right pair of eyes, can change what the whole world can afford to wear.