The stereographic glass negative from President Abraham Lincoln’s last photo sitting, thought to have been Feb. 5, 1865, two months before his assassination. (Gary L. Phillips/Cowan's Auction Inc., Cincinnati, Ohio)

A wet-plate collodion glass negative of a famous portrait of a seated, thoughtful President Abraham Lincoln is scheduled for auction June 21 at Cowan’s Auctions Inc. in Cincinnati, according to the auction house.

Believed to have been taken Feb. 5, 1865, by photographer Moses P. Rice, who worked for Alexander Gardner, it is the last known portrait of Lincoln taken at the Gardner studio before the 16th president was assassinated.

Although Lincoln had been photographed at other studios, he seemed to favor Gardner, who had his business on Seventh Street at Pennsylvania Avenue NW in the District, between the White House and the U.S. Capitol.

However, the well-known portrait was printed from a single-image negative while the one for sale is a stereoscopic negative, meaning there are two images side-by-side. The pose in each looks identical. According to the auction house, Rice made many prints from the single image but does not appear to have printed any pictures from the stereoscopic glass plate.

 “Perhaps the negative size was too small to enlarge [or], more likely, there was little demand for stereoscopic prints,” the auction house said in offering possible reasons for its pristine condition.

  It is very rare for a negative of a Lincoln portrait to be available for sale. This one was passed down through Rice’s family. Cowan’s suggests that it may sell for as much as $60,000.