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What seemed to be a lavishly illustrated manuscript for “the first American opera”, the Revolutionary War oratorio The Temple of Minerva,/i>, as well as a number of marches, songs and poems by the 18th century poet and song-writer Francis Hopkinson (1731-1719), are now thought to be the work of an infamous Philadelphia forger, Charles Bates Weisberg, who died in prison in 1945.

Freeman’s rare books specialist of 20 years David Bloom took the decision to withdraw the collection of notebooks, lyrics, pen and ink drawings and musical folios two days before the sale after consulting Keith Arbour, an independent historian in Cambridge, Massachusetts, who specialises in 18th century printing techniques.

Arbour found a number of discrepancies and inaccuracies in the documents to support the findings of other experts who had raised the authenticity questions in the Philadelphia Inquirer a week prior to the sale.

One of the pieces in the manuscript was identified as being by the 19th century Russian composer Anton Rubinstein. Many of the poems attributed to Hopkinson were then identified by University of Pennsylvania rare book expert Michael Ryan and his staff as “ditties” by Robert Colvill, a late-18th-century English poet.

Weisberg, a brilliant forger who conned dealers and collectors of rare books in the 1920s and 1930s, ultimately received a heavy fine and two and a half years in a Philadelphia jail for another failed forgery.

It was Weisberg’s genius not to attempt to recreate the handwriting of the famous author but instead to suggest his work was a contemporary copy written in an anonymous hand. What falsely convinced Bloom of the authenticity of this potentially important cachet was a letter – found alongside the manuscripts – to the late-18th century Philadelphia publisher Benjamin Carr that suggested that the poems and music were being prepared for publication only a few years after Hopkinson’s death.

Weisberg probably created and sold the documents at least a decade before he achieved his early 1940’s notoriety – perhaps soon after a Hopkinson biography was published in 1926 bringing the Revolutionary figure into the public eye once more.