A portrait by John Opie of John Knill but completed by another hand after the artist’s death sold for £12,000 at the David Lay auction on May 2.

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It depicts John Knill (1733- 1811), a lawyer, customs collector and Mayor of St Ives who was responsible for building the town’s first pier during his time in office before making his fortune as inspector of Jamaican ports.

An eccentric character, Knill commissioned his own memorial, a 50-ft-high granite obelisk called Knill’s Monument, on Worral Hill in the Cornish harbour town in 1782. It still stands.

The 2ft 3in x 20in (69 x 50cm) oil on canvas, inscribed and dated 1777, came to Penrose via Knill’s half-sister Mary Jope, who married John Rogers of Penrose (1778-1856). On the day, it drew multiple bids against a £1000-2000 guide before it was eventually secured at £12,000.

Opie, who was nicknamed locally during his lifetime as the ‘Cornish Wonder’, was just 16 or 17 when he started this portrait in 1777. It was left unfinished when Knill went to Ireland that same year but completed by another hand after Opie’s unexpected death in 1808 aged 46. It is possible the shock of his sudden passing caused a surge of interest in his work, which motivated another artist to finish this portrait.