Gutenberg Bible
Sonne was an expert on the Gutenberg Bible's history and provenance. "A specialist on the Gutenberg Bible, Dr. [Niels H. Sonne] retired as the seminary's librarian in 1976 after 26 years." A copy held by the General Theological Seminary was studied, and found to have a forged page. An anonymous donor to the seminary gave an original page from an imperfect copy of the Bible, thus becoming the first imperfect copy of the Gutenberg Bible to be made whole again.