On September 23, 1933, a tusk was discovered in a gravel pit four miles south of Hampton, Iowa. After careful analysis, the tusk was determined to belong to a Mastodon americanus.1 The University of N..
On September 23, 1933, a tusk was discovered in a gravel pit four miles south of Hampton, Iowa. After careful analysis, the tusk was determined to belong to a Mastodon americanus.1 The University of Northern Iowa museum records note that the tusk was patched with a prepared patching plaster in the 1960’s.2 In the United States at the time Alvar was the most commonly used consolidate to form a plaster. It was either mixed with acetone, alcohol and other solvents, or asbestos.3 The museum record notes indicate that the patching plaster was prepared in a can, like a spackling compound.2 It is unclear whether this is a professionally mixed conservation material, or a product purchased from a hardware store. In either case, the chance that the plaster compound contained asbestos is extremely high. Asbestos is a term used for a naturally occurring fibrous mineral of many types. These crystalline minerals consist of atoms that are arranged in a long-range order and are antistrophic. Due to this, asbestos fibers are polarizable, and can be seen and counted using Polarized Light Microscopy (PLM). If the fibers are too small and not visible via PLM, a Scanning Electron Microscope (SEM) can be used to identify the smallest fibers.4 The Occupational Safety and Health Administration (OSHA) has defined the Permissible Exposure Limit (PEL) for asbestos at 0.1 fiber per cubic centimeter of air per eight hours5, and the OSHA content limit is 1.0% in a bulk matrix.5