Breakthroughs: Anthropology

Tuesday, July 01, 1997
Wind, sun, and rain, not to mention pollution, aren’t kind to limestone and marble, as this pitted visage of George Washington in a Greenwich Village park attests. Conservationists from New York’s Metropolitan Museum of Art, working with chemists from Sandia National Laboratories in Albuquerque, New Mexico, may have found an effective way to stop such decay. Limestone and marble are composed largely of calcium carbonate. To protect the mineral, the researchers first apply a thin wash of a chemical called aminoethylaminopropylsilane, more mercifully known as aeaps, that seeps into microscopic cracks in the stone and binds to calcium carbonate. They next apply a chemical called a sol-gel, which is similar to glass. Sol-gel has been used for years as a protective outer layer on limestone, but it doesn’t bind well to calcium carbonate and quickly wears away. Sol-gel does, however, bind well to aeaps, and together the two molecules seal even the tiniest surface fractures, giving treated stone ten times the longevity of unprotected rock. We’ve done preliminary tests on limestone used in buildings in Bath, England, says Sandia geochemist Kathryn Nagy. It is a very unconsolidated limestone--you can break it with your hands--but this protected it.
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