A protective finish on the most exposed edge
A closed book’s page edges are easy to overlook, but they are exposed to dust, fingerprints, and changes in moisture whenever the book is handled or stored. Unlike the printed faces of the pages, those edges are usually unprotected paper. Gilding them—covering them with a very thin layer of gold—gave the vulnerable surfaces a smoother, less absorbent finish.
The coating could help limit grime and moisture from reaching the paper edges, reducing one route by which pages might become stained or deteriorate. It was a protective measure, not a seal that made a book immune to damp conditions.
How the shine was made
To gild a book, a binder first brought the page edges together and held them firmly in place. The surface had to be prepared so the thin gold leaf would adhere evenly; after application, the gold could be rubbed smooth and polished. The result was a continuous-looking metallic surface along the top, side, or bottom of the closed book.
Gold suited the job because it resists tarnishing, so the edge could keep its bright appearance rather than darkening like many other metals. The process also took skill and time, making gilt edges a visible sign of careful, expensive bookbinding. Their shine was both ornament and a practical finish for paper exposed at the book’s edge.
