Marble structures from India’s Taj Mahal to Italy’s Colosseum are constantly ravaged by pollution and the damaging effects of weather and time. But now, researchers at Princeton University’s Department of Civil and Environmental Engineering have developed a new way to help protect and preserve these iconic structures—by the skin of our teeth.
Researchers discovered that hydroxyapatite, the main compound within human bones and teeth, can be used to protect marble without changing the stone’s color or reflectivity. Marble is made of the mineral calcite, which reacts to a phosphate salt water solution to naturally create the protective hydroxyapatite. The special salt water can penetrate deep into the stone, where the chemical reaction naturally seals cracks and strengthens the marble.
"In spite of being apparently very durable, marble is actually sensitive to several deterioration processes," said Enrico Sassoni, a visiting postdoctoral research associate heading the project. "Environmental temperature variations cause the opening of cracks inside marble, and rain causes dissolution of the carved surface."
But with hydroxyapatite, the marble can stand up better to the elements, staving off crumbling and deterioration. It’s also non-toxic, relatively easy to apply, and takes effect within 24 hours.
The Princeton team is further experimenting with whether the treatment is improved by the addition of alcohol and electric currents. A pilot application of the compound, in collaboration with sculpture restorers, is being planned for sculptures at the Palace of Versailles in France.