A copy of the world's most expensive printed book has sold at auction in London for £6.5m ($10.3m), but why is John James Audubon's Birds of America such a collectors' item?
If you ever see a copy of Audubon's Birds of America lying round a junk shop, you should consider buying it.
It should stand out. The largest version of the book was in what printers call double elephant folio - an enormous 39.5 by 26.5 inches (100cm by 67cm), to allow lifesize illustration of birds.
Even by today's standards, the vividness of its illustrations of birds is extraordinary but when it was being released in the 1830s it was mindboggling. It is perhaps no great surprise that one of the 119 complete copies in existence should fetch millions.
"Audubon was just a fascinating figure, not only as a great artist but as a naturalist. He wanted to complete this monumental work of art," says Lee Vedder, author of John James Audubon and the Birds of America: A Visionary Achievement in Ornithological Illustration.
"It took a long time but it was amazing what he was able to accomplish. It stands as one of the greatest achievements in ornithological illustration."
Audubon, born in Haiti and largely self-taught, spent well over a decade of his life on the magnum opus, which has prints of watercolours of birds and an accompanying volume of ornithological description.
"He spent so much time in the field observing the habits and the habitats - his aim was to record every species of bird and he succeeded quite well," says Mr Vedder.
"He depicted them in motion and movement, their mating habits and feeding habits. It's like you are seeing the actual bird in real life.
"A lot of the images have the site where he found the birds, the vegetation they would feed on, the trees they would nest on."
Today Audubon's name is synonymous with conservation and natural history, but his methods would raise eyebrows with modern animal lovers.
To start with, he killed the birds he painted.
'Toast of Europe'
"He was one of the most rabid hunters you would have ever found. All of the birds he illustrated in Birds of America he killed," says Mr Vedder.
"He would rig them with wire in order to pose them."
Of course, Audubon's painstaking work had to be funded and in many ways he presaged the ways of the modern artist.
Audubon had a huge flair for marketing. Having had trouble raising money after raising the hackles of the academic community in the US, he departed for England, spending time coaxing backers there and in mainland Europe.
"He had a whole song and dance," says Mr Vedder. "He would travel around with his watercolours, and tended to gravitate towards science institutes. He would set up a makeshift exhibition.
"He was the toast of Europe. He would come in with a bear skin coat, bear grease in his long hair, playing up the whole frontiersman myth that Europeans were fascinated with at that time. They were reading James Fenimore Cooper," he said, referring to the American author of The Last of the Mohicans.
Even by the standards of the day, the printing of Birds of America cost an eye-watering amount of money. Audubon did it on a subscription basis and spent much of his time wowing the would-be buyers.
He also went to great lengths to get printers who could achieve the right standard of reproduction. He went first to Edinburgh before going to London and collaborating with the artist and printmaker Robert Havell.
"The prints are phenomenal," says Mr Vedder. "They really did set a standard for print-making."