Ariel O’Connor, Meg Craft, Glenn Gates, and Julie Lauffenburger
Abstract
A heavily tarnished 19th-century Persian water pipe, or nargile , made of gilded silver decorated with gemstones required cleaning for exhibition at the Walters Art Museum. X-ray fluorescence spectrographic analysis indicated an alloy of silver with copper, gold, and lead. Standard methods for mechanical tarnish reduction were tested, but all produced a silver-colored surface. Further x-ray fluorescence spectrographic analysis revealed that even the gentlest mechanical method—solvent cleaning with a cosmetic sponge—removed gold from the surface. Chemical test cleaning with acidified thiourea, or “silver dip,” removed tarnish and preserved gold, but research has shown problems with this method, including potential leaching of copper, microetching, residual surface complexes, and increased light reactivity. Pros and cons of each method were considered, and thiourea was selected as least harmful. Methods for the safe use of thiourea in this context are discussed, and a new approach with non-woven cotton pads is introduced for cleaning.