CSI Mentioned in Washington Post on Marble Conservation
Q: We have inherited three marble statues that are in need of cleaning. One spent time in an outdoor courtyard and is especially dirty. How can we clean them without damaging the marble? If we cannot clean them ourselves, how do we find a reliable source, and what might the approximate cost be?
A: The most important caveat about cleaning marble is to avoid acidic cleaners, such as vinegar or lemon juice, because they eat into the stone. The safest DIY approach is to wash the stone with warm water plus a few drops of stone soap or clear hand dishwashing soap, then rinse thoroughly with water.
But conservators who have studied stone extensively cringe even at that advice. “Marble can be very porous, and it’s possible to drive in staining materials if the cleaning isn’t done by an experienced conservator,” according to Connie Stromberg of Stromberg Conservation in Bethesda (301-263-9298; firstname.lastname@example.org). Even plain water can slowly dissolve the stone if it is acidic, as rain typically is because its pH is usually 4.5 to 5.5 on a scale where 7.0 is neutral. Conservators rinse with buffered water, raising the pH to about 8.5 with ammonia or calcium carbonate (precipitated chalk). But, Stromberg wrote in an e-mail, “I don’t think I should give ‘how to’ directions for doing that” for fear of damaging the sculpture or the person.
A conservator begins by examining the sculptures carefully and testing cleaning treatments in a small, inconspicuous area before deciding on an approach. A key initial question is what kind of stone is involved. What appears to be marble might actually be alabaster, Stromberg said. Alabaster has an entirely different chemical makeup from marble and can actually be harmed if cleaned with water.
Stromberg looked at the photograph you sent and noted that the statue that was outside appears to be stained mostly near the base. Removing that kind of stain often involves applying poultices to draw it out.
Conservators set their rates individually but are never inexpensive. Stromberg charges $110 an hour and said that cleaning statues like yours would probably take at least a day, meaning the bill could come to hundreds or even thousands of dollars, especially if any repairs are needed or the stone has a finish that needs to be removed to allow the cleaning. When people can’t afford a pricey cleaning, Stromberg says it’s often best to leave statues as-is, because improper cleaning makes the damage worse.
The American Institute for Conservation of Historic and Artistic Works provides a “find a conservator” service on its Web site, www.conservation-us.org. Two near you are Paul Jett in Accokeek (202-467-0214; email@example.com) and Mark Rabinowitz at Conservation Solutions in Alexandria (866-895-2079; www.conservationsolutionsinc.com).