In 1917, working alone in a remote Swiss asylum, psychiatrist Hermann Rorschach devised an experiment to probe the human mind: a set of ten carefully designed inkblots. For years he had grappled with the theories of Freud and Jung while also absorbing the aesthetic movements of the day, from Futurism to Dadaism. After Rorschach’s early death, his test quickly made its way to America, where it took on a life of its own. Co-opted by the military after Pearl Harbor, it was a fixture at the Nuremberg trials and in the jungles of Vietnam. It became an advertising staple, a cliché in Hollywood and journalism, and an inspiration to everyone from Andy Warhol to Jay Z. The test was also given to millions of defendants, job applicants, parents in custody battles, and people suffering from mental illness or simply trying to understand themselves better. And it is still used today.