Among the 550 Leonardo da Vinci drawings in the Royal Collection, there are several sheets that appear blank in visible light. However when examined under ultraviolet (UV) light, the drawings suddenly reveal themselves, as we can see here with this metalpoint drawing 'Studies of hands'.

‘Ultra violet’ means ‘beyond violet’ (from the Latin ultra, ‘beyond’), violet being the colour of the highest frequencies of visible light.

When this drawing was catalogued in 1935, it was referred to as ‘much rubbed’, ‘half-effaced’ and ‘almost invisible’. It was not until the 1950s that conservators at the British Museum and its research laboratory illuminated this drawing with UV light, revealing Leonardo’s study of hands. The results were published as an example of how technical analysis can aid the study of works of art.