Benjamin Franklin's Philadelphia printing shop made plaster molds from pressed sage leaves to create metal stamps for marking foliage patterns onColonial currency. The distinctive contours of leaf spines, stems and veins were meant to thwart counterfeiters, and Franklin's workers managed tokeep the casting technique a secret that has puzzled modern scholars, too.

James N. Green, the librarian at the Library Company of Philadelphia (founded by Franklin in 1731), had wondered for the last two decades if anyof Franklin's actual metal leaf-printing blocks for the bills survived. He had concluded that if one of these castings ever did emerge, it would be"a really sensational discovery," he said in an interview last month.

Such a discovery has been made in a vault at the Delaware County Institute of Science in Media, Pa. Jessica Linker, a historian who is studyingearly female botanists, recognized the sage leaf patterns on one of Franklin's metal blocks when the institute staff opened the box it was stored in.The block is now on loan to the Library Company, which is planning to exhibit it with related printing equipment and currency. Its three parallelsage leaves match images on Franklin's 1760s shilling notes for Delaware's government; the bills bear the slogan "To Counterfeit is DEATH."

Hardly any early American metal printing blocks survive; most were melted down into raw material for new type. Fragments dating to the 1600s havebeen excavated at Harvard Yard, and early-19th-century metal letters surfaced at the construction site for the Museum of the American Revolution inPhiladelphia.

Colonial shillings on paper, however, are relatively common. They bring a few hundred dollars each at auction, as do antique counterfeits.

Artifacts from America's centuries of battles against currency forgers have become popular museum displays as well. Mark Tomasko, a collector andhistorian who has collaborated with institutions including the Museum of American Finance and the American Numismatic Society on related shows, saidthat fake bank notes and the tools used to create and detect them were "a constant interest."

He has sought out material related to the American inventor Jacob Perkins; in the 1790s, Perkins developed steel plates for printing currency thatwere considered nearly impossible to fake. Perkins's engraving plant has been restored in Newburyport, Mass., and the Historical Society of OldNewbury is developing exhibitions there that are scheduled to open in 2016.

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How Franklin Thwarted Counterfeiters(www.nytimes.com/2014/12/12/arts/design/how-franklin-thwarted-counterfeiters-.html)