PROVIDENCE, R.I. — Day after day, a tall, shy woman weaves her way unnoticed through the earnest and learned campus swirl of Brown University. She enters the hush of a library, then promptly vanishes from sight.

Down goes Marie Malchodi, 48, who attended but never graduated from Brown, down to the library’s subterranean warrens, where she works as a “book conservation technician.” She sweeps her long dark hair into a bun, pierces it with a paint brush, and starts her day, caring for ancient books and ephemera that are sensitive to the touch.

A few weeks ago, Ms. Malchodi opened yet another leather-bound book, one of more than 300,000 rare volumes in the hold of the John Hay Library. With surgical precision, she turned the pages of a medical text once owned by Solomon Drowne, Class of ’73 (1773, that is.). And there, in the back, she found a piece of paper depicting the baptism of Jesus. It was signed:

“P. Revere Sculp.”...