1. Museum Conservation Institute, Smithsonian Institution , 4210 Silver Hill Rd., Suitland, MD 20746 , USA
2. Material Measurement Laboratory, National Institute of Standards and Technology , 100 Bureau Dr., Gaithersburg, MD 20899 , USA
3. National Museum of Natural History, Smithsonian Institution , 10th and Constitution Ave. NW, Washington, DC 20013-7012 , USA