If you come across brightly colored, cloth-bound books from the Victorian era, you might want to handle them gently, or even steer clear altogether. Some of their attractive hues come from dyes that could pose a health risk to readers, collectors or librarians.

The latest research on these poisonous books used three techniques—including one that hasn’t previously been applied to books—to assess dangerous dyes in a university collection and found some volumes may be unsafe to handle.