The document fetched $2.09 million, including a $235,000 commission, the second-highest amount ever paid for a copy of the proclamation signed by Lincoln, The New York Times reported.
A Lincoln-signed copy of the proclamation that had once been owned by Robert F. Kennedy sold for $3.8 million two years ago.
David Rubenstein, managing director of The Carlyle Group investment firm, bought the copy that sold Tuesday at Robert Siegel Auction Galleries. The Times said the U.S. seller remained anonymous.
The proclamation, issued Jan. 1, 1863, freed all slaves in states in rebellion at the time and provided a legal route to the emancipation of millions of other slaves. Forty-eight copies were printed after Lincoln issued the proclamation, and he signed all of them in 1864, with copies sold throughout the United States to support Union troops.
"They have appreciated in value because it's so powerful as a document," said Seth Kaller, an expert in U.S. historic documents who worked with the seller in Tuesday's auction. "If you have an original document like this on exhibit, people get a sense of the excitement. This document changed the course of history."
Kaller's Web site, www.SethKaller.com, lists the location of 26 copies of the proclamation, 18 of them in museums and libraries.
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