The Tate acquired a painting in 1995 that they knew little about, according to the Telegraph:

But a stencilled lot number on the canvas was found to refer to a Christie’s sale in 1929, when the artwork – dated 1655-9 – had been described as “Portrait of Mrs Dobson, of West Peckham, Kent, and her son, Thomas Dobson, in a landscape with Satyr and Cupids”.

Yet there was nothing cherub-like visible on the canvas. The mystery was resolved when an infrared photograph was taken, which revealed two Cupids holding a wreath, together with a rose being thrown into the lady’s lap and a theorbo – a long necked lute – at the right of the painting.

Careful cleaning and restoration by Helen Brett, the Tate Paintings Conservator, uncovered the original composition, which is thought to have been overpainted around 70 years ago.

Angels Uncovered in 350-year-old Painting (Telegraph)