Paper—a relatively flat sheet of bonded cellulose or plant fibers—can be surprisingly strong and long-lasting. Like most organic materials, it is vulnerable to decay from poor environmental conditions such as extreme humidity or heat. Acidity from pollutants in the fibers, applied media (such as ink), or surface dirt and oils from handling can also cause deterioration.

Book and paper conservators use treatments such as surface cleaning, deacidification, and aqueous treatment to mitigate damage. Aqueous treatment involves submerging paper in one or more baths of clean water to reduce acidity, lighten discoloration, and remove dirt. It is also effective for removing certain tapes and adhesives, such as paper tape with water-soluble adhesive—if the paper and media can withstand immersion. Media must be tested for water solubility before treatment proceeds.

This 1807 map of Boston from The Life of George Washington had been attached or mended with paper tape. After solubility testing confirmed it could be immersed, the map was placed between sheets of Hollytex—a thin, strong, acid-free polyester—for support. Once humidified to relax fibers, it was submerged in a water bath. Gentle pressure encouraged absorption, and after about 30 minutes, the adhesive softened. The tape was peeled back and any residue removed with a microspatula and plastic spatula.

The map then underwent several clean baths to further reduce acidity and discoloration. After the final bath, it was air dried flat on a blotter. It will be mended and hinged back into the book with Japanese paper and starch paste. Washing has removed much of the acidity, strengthening the map for many more years of use.