X-ray evidence of Black maths scholar portrait reveals snubbed genius

Francis Williams c1745, oil on canvas. The portrait was bought by the V&A’s furniture curator in 1928, primarily because it depicted fine mahogany furniture. Photograph: Paul Robins/Victoria and Albert Museum, London

It was painted to celebrate the groundbreaking achievements of a mathematical genius who was Black and had been born into slavery. But for more than 260 years, that great scientific intellect of Francis Williams went unnoticed.

Now, clues exposed by an X-ray and high-resolution scans of the painting have finally revealed the extraordinary secret that 18th-century advocates of slavery sought to keep hidden.