One of the questions that surrounds art as an asset is how to quantify an income stream from any sort of collection. But a recent report from Colin Gleadell suggests that art—in this case, 580 paintings and drawings assembled lightning quick over a three-year period—can produce revenue on an indirect basis. Roger Tempest and his company, Rural Concepts, bought a Scottish manor on the shores of Loch Ness. The house had been in the same family for generations but when the last family member died in 2004 it was sold and the contents disbursed throughout the family.

After a lengthy planning process, Tempest then embarked on a reported £10 million restoration programme. By October 2009, the 57-room castle had been restored down to the last bath tap, and opened for business as a destination for holidays, house parties and corporate functions, which rents out at about £21,000 (plus VAT) a week.

A major part of the renovation was assembling an art collection that would complete the home’s appeal:

For Old Masters, Tempest wanted to create the feel of a house where the owner had been on a Grand Tour, returning with his trophies.

Here he consulted Alec Cobbe, a picture restorer and designer for historic homes, who had previously re-hung the art collections at Petworth House, Kenwood and Harwood. Cobbe kept his eye on minor sales, and last year he bought a rare Holy Family by the 17th-century French classicist Sebastien Bourdon, at Christie’s for £31,000.

At Sotheby’s, Cobbe spotted a dark painting, supposedly of Diogenes, by the Italian baroque artist Salvator Rosa, which was snapped up for £39,650 and improved with cleaning, and a Madonna and Child, which he recognised as a variant on a similar composition in the Louvre, by the 17th-century Bolognese painter Lorenzo Sabatini, for £18,750.

Copies were not anathema to 18th-century collectors, and at Aldourie there are a number, notably a recent copy of Raeburn’s famous The Skating Minister, and an 18th-century copy of Raphael’s Madonna of the Pinks.

Such a rich mixture of originals, discoveries and copies are not only stimulating, they create an illusion of authentic, historic grandeur, and so make that prize more deserved and that rental seem all the more worthwhile.

Art Sales: The Treasure  Trove on the Loch (Telegraph)