Among the treasures in the Harvard College Library Map Collection are two globes produced by the Flemish cartographer Gerhard Mercator (1512-1594). The terrestrial globe, produced in 1541, and the celestial globe, produced in 1551, are the only known matched pair of Mercator globes in America.

The terrestrial globe (above) is from 1541. The celestial globe (below) was produced in 1551. They are the only known matched pair of Mercator globes in America.

Renowned for his skills as an engraver, calligrapher, and maker of scientific instruments, Mercator produced distinguished maps, atlases, and nautical charts throughout his adult life and invented the Mercator projection.

Among the distinguishing features of the globes is the innovative way in which they were constructed. Twelve copper-engraved paper gores and two circular paper pieces (for the north and south poles) are contoured to cover each plaster-coated, hollow sphere as completely and accurately as possible. Mercator's creativity, command of mathematics and geography, and artistic skill yielded globes of unprecedented quality.

No other editions of the Mercator globes were produced after the first, and few survive. Until this year, Harvard's globes were in severely deteriorated condition. Tide marks (water damage), stains, pronounced surface grime, degraded varnish, fly specks, and abrasion defaced both terrestrial and celestial spheres and their accompanying faux marble painted stands. The paper gores on the celestial globe were separating in places and lifting along the seams. The paper component of both horizon rings was weak, brittle, and discolored. Losses revealed underlying wood.

The wooden stands on which the globes rest were insecure because of breaks in supporting dowels. Cracks, nicks, and losses were apparent in the legs of the stands and along the outer edges of horizon rings. Brass components were soiled and tarnished, and revealed remnants of polishing solution.

Generous gifts from J. Christopher Flowers (A.B. '79) and Mary H. White via the White Flowers Foundation; and from Carl H. Pforzheimer III (A.B. '58, M.B.A. '63) and Betty Pforzheimer have funded full conservation treatment of Harvard's two Mercator globes. The work was carried out by T.K. McClintock Ltd. (Conservation of Fine Art and Historic Works on Paper). The Society for Preservation of New England Antiquities Conservation Center restored the wooden stands.

Extensive research usually precedes the development of a treatment plan for complex artifacts, and this was certainly true with these globes. Each was photographed and X-rayed.

Varnish was analyzed, and paint samples from the wooden stands were examined in cross-section using ultra-violet microscopy. A pair of globes in Duisburg, Germany, and a set of unmounted paper gores in Brussels, Belgium, were examined to learn more about the nature of original construction materials and finishes.

Over the course of treatment, grime was removed from paper surfaces using several complementary strategies. Loose sections of paper were re-adhered, tidemarks reduced using moisture poultices, and brass components cleaned using appropriate solvents.

Paper losses were replaced with paper similar to the original in texture and weight, which has been toned to match surrounding paper, lined with Japanese paper, and adhered with wheat-starch paste.

Restoring the wooden stands involved stabilizing loose joinery, removing grime, removing darkened overvarnishes as necessary, inpainting losses, and other treatments.

All materials used for cleaning and restoration have been carefully selected for long-term stability and appropriate aesthetic characteristics.

As complicated as it may sound, the treatment is conservative. The goal is not to make the globes look new, but rather to improve their legibility, protect them from further damage, and ensure that they remain usable for centuries to come.

David Cobb, head of the Harvard College Library Map Collection, remarked of the project, "Maps are a reflection of the culture that produces them. These globes reflect the art and science of the 16th century, and for the students and scholars who will use them they are a window on the past."

Nancy M. Cline, Roy E. Larsen Librarian of Harvard College, commented, "The Library has many rare and exceptional items that are of great value to scholars, but that require preservation treatment if they are to sustain any level of use. The 16th-century knowledge of the world and of the universe, revealed so elegantly in these Mercator globes, remains a reference point for many fields of study."

Continued Cline: "It was exciting to watch the restoration work progress, to see once again the detailed notations and drawings on these globes, and to know that future generations of researchers will be able to consult them."

Cobb said he has had discussions with a firm in Baltimore about building a case for the globes that would allow the library to exhibit them safely. The case would have special non-destructive lighting, atmospheric filters, and temperature and humidity controls.

"The globes are quite unusual and quite rare. It would be a shame to hide them away after doing all this restoration work," he said.