One of the 16 rediscovered Samuel Scott watercolour drawings sold by Thomson Roddick in Rosewell, Edinburgh on December 4. The Thames wharf and shipbuilding with Westminster Bridge beyond, 14 x 2ft 11in (36cm x 90cm) which made £52,000.

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Unearthed in a tea chest were 16 topographical drawings by the 'father of British watercolour painting' Samuel Scott (1701/2-72). They were unframed, unsigned and, sometimes, unfinished, but when picture specialist John Thomson researched them, he also found them to be unpublished works that do not feature in Richard Kingzett's 1982 catalogue raisonné of Scott's oeuvre.

The family in whose home the works were found had been utterly unaware of their existence. It emerged after the sale that the family had ancestral links to the Bristol and Bath area where, sometime around 1766, Scott retired with gout.

The drawings had been stored for at least two generations, folded under a pile of books which appeared to have preserved them in reasonable, rather than good, condition and all required conservation.

These watercolour, pencil and ink sketches on joined paper - some over 3ft (91cm) across and with ink annotations in the artist's hand - were predominantly views of the Thames, presumably preparatory works for the oils Scott painted at his Covent Garden studio.

The fact that a number of these highly detailed drawings in the manner of the van de Veldes apparently relate to major finished pictures, means they probably date from the mid-1740s.

It had been the arrival of Canaletto in London in 1746, and the stimulus he gave to the demand for London views, which prompted Scott to extend his talents from marine painting to the topographical views of the Thames and its bridges for which he is now best known. As a painter in oils, Scott has commanded very substantial sums: the Wills sale at Sotheby's in July 2005 included some outstanding pictures by him, including a 1746 oil of The Thames at Westminster Bridge with barges, which sold for a premium-inclusive £1,632,000.

However, drawings and watercolours appear less frequently, and works of this unusually large scale are extremely rare.

A 13 x 23in (33 x 57cm) watercolour of Twickenham from the Thames, 1758, which made £8500 at Sotheby's in June, provided Thomson Roddick with their guidelines, although the pictures were offered without reserves.

In fact, the exceptional cache of rediscovered pictures collectively sold for more than £300,000 with ten works making five-figure sums. There were two principal telephone buyers.

Agnews' Christopher Kingzett (whose father wrote Scott's catalogue raisonné) bought a number of works, including one of the large London views, A Wood Yard by the Thames at Nine Elms, 131/2in x 2ft 11in (34cm x 89cm), at £50,000.

They were the underbidders to another London dealer on a further 11 works, including a view of shipbuilding on a Thames wharf with Westminster Bridge beyond knocked down at £52,000 - a price shared with another view of buildings by the Thames which could well be an auction record for a Scott watercolour.

For more on watercolours and drawings, see the Art Market section this week's printed newspaper. To subscribe, click here.