Tom Lingenfelter, of suburban Doylestown, has spent years researching the document, which he bought at a flea market for $100. He said he believes it to be an anastatic copy made in the 1840s through a then-novel printing process designed to make instant copies. The only other known anastatic copy was found at Independence Hall.
"This is like finding a haystack and then finding the needle," Lingenfelter said of his research.
His copy will be on display Monday afternoon at the historic Moland House in Hartsville, in Bucks County.
In the anastatic printing process, which reached the U.S. in the 1840s, an acid-based solution was used on documents to make negatives on zinc plates that were then copied on a printing press. But the process damaged originals, including the hand-signed Declaration of Independence that Lingenfelter said then hung on a wall at the U.S. patent office in Washington.
National Park Service curator Robert Giannini agrees the copy is nearly identical to the one found at Independence Hall. Both mirror the size of the original, about 25 by 30 inches, he said. And both had frames made from timbers from Independence Hall, according to Lingenfelter, a longtime dealer in historical documents and artifacts.
Giannini said: "There are only two of those that I know of. That alone would probably make them fairly valuable."
Thomas Jefferson drafted the Declaration of Independence, which announced the colonies' independence from Great Britain, in a room he rented two blocks from Independence Hall. Printer John Dunlap hurriedly printed the broadsides after the 13 colonies approved it on July 4, 1776. Twenty-six Dunlap originals are thought to exist. One sold for $8.14 million to TV producer Norman Lear and a partner in 2000.
"Mine is more rare," Lingenfelter said. "It's a direct copy of the original."
The original - a hand-crafted parchment copy signed by each member of Congress - wasn't finished until mid- to late August 1776, Giannini said. That is the engrossed version, now badly faded, displayed at the National Archives.
Lingenfelter did not originally consider his find especially significant, and he took it to his daughter's elementary school years ago to show students. He guessed it might be a reprint made for the 1876 Centennial Exhibition in Philadelphia.
"I didn't take particularly good care of it," he said.
Later research leads him to conclude it was made by John Jay Smith, a prominent Philadelphian who had bought a license to bring the process to the U.S. from Europe in 1846. Smith hoped the formula for making instant facsimile copies would prove profitable because it could take printers weeks or months to typeset large orders.
And it proved popular for a few years, drawing praise from Edgar Allen Poe, among others.
"He thought it was a miracle of scientific discovery," Lingenfelter said.
But the process was messy, and the wet solution loosened ink on the originals. The dawn of photography, meanwhile, and newer printing techniques soon hastened its demise.
"Any wet solution would immediately cause ink to fall off or at least loosen the ink," Lingenfelter said. "You should never use the process if you're trying to save the original."