The Mercer family’s fortune started in the eighteenth century in England, increased via South African gems in the nineteenth, and is managed on an ethical basis today. When a modern Mercer begins digging beneath the surface of their history, the family’s past suddenly appears less clear-cut than the gems they once traded. Luminosity links a physic garden, a fabulous diamond and the colour of skin; exploring race and identity and the moral responsibility of representing the past.