In May 2010, a tattered and brittle map was discovered in storage at the Brooklyn Historical Society. Experts identified it as a rare item, a Bernard Ratzer “Plan of the City of New York” map in its 1770 state.
Ratzer is known as something of a Da Vinci of New York cartography, and the map was an early edition of his best-known work. A British Army officer in America, Lieutenant Ratzer was a surveyor and draftsman, and his map was immediately praised as a step forward from those of his predecessors. Only three other copies are known to exist.
The map was in disastrous shape. After a painstaking restoration to remove layers of shellac and grime and repair dozens of breaks, the map is now behind plexiglass and ready to be displayed to the public.
You can read about the restoration at http://www.nytimes.com/2011/01/17/nyregion/17map.html?_r=1
My thanks to Hal Miller for telling me about this story.