It also brought "a fundamental change in the character of the war," Washington said. "With the stroke of Lincoln's pen, a war to preserve the union had overnight become a war of human liberation."

The proclamation became a symbol of hope for nearly 4 million slaves and a confirmation that the war should be fought to secure their freedom, said Washington, who is retiring from the Archives after nearly 40 years. Some historians and scholars have come to view to proclamation as one of the most important documents in U.S. history.

The final proclamation has been rarely shown because it was badly damaged decades ago by long exposure to light. After it was signed at the White House, it was kept at the State Department for many years with other presidential proclamations. In 1936, it was transferred to the National Archives.

Records show it was displayed between 1947 and 1949 in a "Freedom Train" exhibit that traveled the country. Then it was shown briefly in January 1963 to mark the 100th anniversary of its signing.

It wasn't until 1993 that the Emancipation Proclamation has been shown more regularly to the public. In the past decade, it has been shown in 10 other museums and libraries nationwide for no more than three days at a time to limit its exposure to light. A 2011 exhibition at the Henry Ford Museum in Dearborn, Mich., that was open around the clock drew lines amounting to eight-hour waits to see the document.

Conservators rotate which of the five pages are shown to limit their light exposure. In Washington, they will display pages two and five, which is Lincoln's signature page. High-quality copies are shown in place of the other original pages.

"It's rarely shown, and that's part of our strategy for preserving it and making it accessible," said Catherine Nicholson, an archives conservator. "Our goal is to keep its current condition so that it can be enjoyed not only by people today, but by future generations."