An untitled painting by Mark Rothko is among the highlights of Sotheby's Bear Witness sale in London on March 10-12.

The work, produced on paper and dating to 1968, carries a valuation of £3m-4m ($4.6m-6.1m).

Mark Rothko was a pioneering abstract expressionist painter

While Rothko is best known for his enormous canvases, his works on paper are considered very much their equal. They offer an intimacy lacking elsewhere in his canon and have been extensively studied and exhibited over the years.

B Clearwater, in his book Mark Rothko: Works on Paper, comments: "Rothko never abandoned bright colours in his works on paper, the late vibrant paintings on paper contain a force not experienced in earlier small works ��? these late creations, with their dense unmodulated surfaces, do not flicker with light; rather, they generate a strong, constant glow."

Edward Ruscha's I CAN'T NOT DO THAT is valued at £1.2m-1.8m ($1.8m-2.7m).

The piece comes from Rucha's word paintings series, which he has been producing since the early 1960s. Last year SMASH, a piece from 1963, sold for a record $30.9m at Christie's New York.

In addition to works from leading artists, the sale includes curios with estimates as low as £20 ($30). The collection belonged to a single owner who had something of a soft spot for bears and skulls.

Sotheby's Alex Branczik comments: "This truly idiosyncratic collection is a modern day Wunderkammer, assembled to inspire and amaze. Crossing every continent, from Mexico to Japan, Indonesia to China, "Bear Witness" encompasses everything from the contemporary to the curious."

"Quite possibly the most extraordinary exhibition Sotheby's has staged in its 270-year history - it is a unique opportunity to see works by the likes of Hirst, Warhol and Koons alongside the objects and ephemera that inspired them."

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