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This privately-owned watercolour of Harlech Castle has not been seen by the public at large since the late 19th century

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Turner produced many views of England's ruins, such as this Yorkshire abbey, pictured from another private collection

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One of many commissions he received for country house views, this study of Chalfont House came to light last year

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A meditation on colour and light in the Swiss Alps, The Dark Rigi is another privately-owned watercolour

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On display at a museum in Japan, this atmospheric later work is inspired by 17th century French artist Claude

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An early view of Margate, Kent, where Turner often later stayed, inspired by the changing moods of the sea

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From a series of views of Farnley Hall, painted for owner Walter Fawkes, patron and friend of the artist