Summer 2017

the use of chemical cleaners over generations can significantly alter a clock’s metal elements, often to the point of no return. Understanding previous cleaning techniques in order to attempt to reverse their negative effects was our challenge for Winterthur’s tall clock with a dial signed by Benjamin Chandlee (Fig. 3). Some might describe the dial’s patina as original or “untouched,” but the brass dial and silvered elements were nearly the same color as the walnut case. Just the fa intest trace of green copper oxidation was visible, and the thin layers of silvering could only be detected by scientific instruments. Rather than aging through gentle neglect, these metal surfaces became uniformly copper y-pink due to assiduous, harmful cleanings that resulted in a zinc depletion that altered all the surfaces especially in the formerly silvered areas (Fig. 4). Before attempting to improve the dial’s appearance, conservation fellows Lauren Fair and Jessica Arista identified black fill material in the dial’s engraved numbers and signature boss as pine resin, beeswax, and bitumen. Protecting those delicate original black fills was a priority that further complicated their treatment. They also determined that gentle elbow grease and cotton swabs alone would not return a warm, yellow surface to the brass. After disassembling all the dial components, gentle chemical cleaners tailor-made in our lab were imbedded in a gel and selectively applied. 3 Gradually the brass elements released the contents of their corroded surfaces and cleaning continued. The black-filled numbers received protective barrier coatings and any losses were filled in with acrylic paint. For the elements originally silvered, we selected a water-soluble gilding method using palladium leaf for its fully reversible quality and gentle, aged look. This experimental, time-consuming process yielded an elegant clock dial, once again harmonious with its original case (Fig. 5). While our method was designed specifically for this particular brass dial, thankfully, the painted and varnished wood dials favored by Seth Thomas and other manufactories are less complicated to clean. The lesson here is that residues from 2017 Antiques & Fine Art 143 chemical cleaners can continue to alter surfaces even if they are invisible. Other than careful dusting, antique clocks are best cleaned by professionals.  Ann K. Wagner is curator of decorative arts at Winterthur Museum, Garden & Library, and co-curator, with Josh Lane, of   Striking Beauties: American Shelf Clocks and Timepieces. 1. The inspection was undertaken for the exhibition Striking Beauties: American Shelf Clocks and Timepieces, that was on view from July 2, 2016–April 9, 2017. 2. Commercial polishing products often contain ammonia, which should be avoided when cleaning brass. The pH of any cleaning solution needs to be considered when cleaning copper alloys, as highly acidic solutions can solubilize zinc and weaken the metal substrate. 3. The cleaning process we selected is not typical, but is currently being explored by conservators. Figs. 3, 4, 5 : Tall clock with 8-day movement, Benjamin Chandlee Jr. (1723–1791), Nottingham, Pa., ca. 1755– 1875. Museum purchase with funds provided by the Henry Francis du Pont Collectors Circle (2003.32).