David Bowie's art collection is going on tour. Three hundred and eighty of the late star's paintings, including works by Jean-Michel Basquiat, Frank Auerbach and Damien Hirst, are on view at Sotheby's in London before being brought to Los Angeles, New York and Hong Kong for viewings.

Back at Sotheby’s, they will be auctioned on November 10th. The collection is expected to fetch $13.3 million (€11.9 million). And it’s not even all of Bowie’s art collection: his wife, Iman, kept back his most prized pieces.

The Sotheby's and Christie's auction houses are now the place where the real money is to be made from the music industry. Two years ago, Bob Dylan's handwritten lyrics to Like a Rolling Stone sold for $2.1 million at Sotheby's – a still-standing world record for a popular music manuscript.

Musical acts who may have been dismissed as tuneless, long-haired, degenerates early in their career are now the blue-chip lots in auction houses. The personal possessions of acts such as the Beatles, Dylan and Bowie, who have had a major cultural impact and will continue to do so for generations to come, are among the most coveted by auction houses.

The people bidding millions for a piece from the Bowie personal art collection in Sotheby’s in November will be able to proudly boast that their newly acquired work used to hang in the singer’s downstairs toilet.

There remains such an aura around a handful of pan-generational popular musical acts that anything they have themselves created or previously owned takes on a financial lustre for buyers.

This September John Lennon's Austin Princess Limousine Hearse, as featured in his 1972 film Imagine, is expected to realise more than $400,000 at Sotheby's.

But this is in small compared with the price fetched for a Rolls-Royce Phantom V that Lennon bought in 1965. He painted it in psychedelic colours and often loaned it to his famous rock-star friends. At auction in 1985, it sold for $2.3 million but if it were to be sold today, it would fetch more than $20 million.

Again, the fact it was used by Lennon, Dylan and the Rolling Stones adds value to its auction price.

Guitars that once belonged to Eric Clapton fetched $5 million at Christie's in New York back in 1999. You can multiply that figure to find out what they are worth today.

Artistic worth

All of which doesn’t necessarily mean that a bikini worn by Rihanna in a video shoot, or a hoverboard as used by

Katy Perry

, are worth hanging on to – supposing you were strange enough to have them in your collection in the first place. The person must have artistic worth over decades and be regarded as a significant contributor to the cultural canon before their possessions achieve multimillion financial worth.

But with some notable rock star autographs going for hundreds of thousands of euro and even a lock of their hair being able to command an impressive price on eBay, this really has become a "cash in the attic" area.

There is still the impression that leading auction houses such as Sotheby's and Christie's are really interested only in a Da Vinci or a Constable, but just last year Sotheby's sold a Sex Pistols signed record contract from 1977.

It is interesting to note that the most prized piece in Bowie's art collection, which is expected to fetch $5 million at the November auction is a 5ft high 1984 painting by Basquiat called Air Power. To put that $5 million price tag in context, Bowie bought the piece in 1995 for just $120,000.

Outside the art world, not that much is known about the US neo-expressionist Basquiat, who died from a heroin overdose at just 27 (interestingly Bowie, played Andy Warhol in a 1996 film of his life).

Mystical allure

In rock music circles, though, Basquiat has a mystical allure. U2 spotted one of his works in New York in 1989 and for almost 20 years their Basquiat hung on the walls of their recording studio on Hanover Quay, Dublin. In 2008 they sold it for $6.5 million at Sotheby’s.

Metallica's drummer, Lars Ulrich, bought a Basquiat in 1999 for, as he says himself, "just a couple of a million dollars". In 2008 he sold it at auction for $13.5 million.

The fact that both U2 and Ulrich both sold their Basquiats in 2008 may have had something to do with that year’s financial crisis and fears of how it would impinge on the art market.

Two months ago, in May 2016, Christie’s broke its auction record when it sold a Basquiat for $57.3 million to a Japanese businessman.

All of which makes you think that Bowie’s Basquiat being sold in November with an estimate of $5 million may be quite the steal.