Two sculptures by Barbara Hepworth are being consigned by her former school in Wakefield, UK.
They will sell at Sotheby's London on June 13.
Forms in Movement (1956) is valued at £250,000-350,000 ($361,885-506,639), while Quiet Form (1973) is expected to make £500,000-700,000 ($723,770-1m).
The former was bought by the school for the opening of a new gym in 1956, while the latter was commissioned as a retirement gift for a head teacher.
Frances Christie, Sotheby's head of modern & post-war British art, comments: "Hepworth is the only British female artist to have two galleries dedicated to her, and following a hugely successful retrospective at the Tate Britain last year, the appetite for the very best examples of her work has never been stronger.
"We are thrilled to be offering two beautiful objects with such a great story of personal importance to one of the giants of 20th-century art."
Hepworth was always grateful to her school for encouraging her to develop as an artist.
Her head teacher, Miss McCroben, helped her achieve a scholarship to Leeds School of Art and arranged lodging at London's Royal College of Art.
John McLeod, a spokesman for the school's board of governors, explained the decision to sell: "As Hepworth's market prices have rocketed, so have the costs of insurance and security.
"While this means that it is hard to justify devoting valuable—and limited—school resources to insurance costs, it also means that we have the unexpected opportunity to release significant funds, which can be used to afford other students just the kind of special opportunities Barbara Hepworth enjoyed through bursaries."
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