Robin O’Hern and Kelly McHugh
Abstract
This article presents the results of two surveys focused on the condition and treatment of deteriorated glass beads in the collection of the National Museum of the American Indian (NMAI). Glass deterioration occurs when hygroscopic alkali components of the glass migrate to the surface and form salts. The leaching of alkali components leaves a silica enriched surface layer, which is vulnerable to further deterioration. Environmental parameters, glass composition and manufacturing processes, contact with other materials, and previous use of the object can all affect the deterioration process. Because of the large number of beaded objects at the NMAI, glass disease is a collection-wide condition issue.
Two targeted collections surveys were, therefore, carried out to monitor condition change and treatment results for at-risk beads. To assess changes in condition over time, a selection of objects originally surveyed in 1999 were re-surveyed in 2013. Ninety percent of the beads had no visible change to the deteriorated glass over 14 years. A second survey was conducted to evaluate whether treatment options used for blue and red beads—cleaning with deionized or distilled water, ethanol, 1:1 deionized or distilled water: ethanol, or mechanical cleaning—had different long-term results. Approximately 50% of the beads cleaned with water or 1:1 water: ethanol and 47% of beads cleaned with ethanol redeveloped glass deterioration; however, if the results for beads cleaned with 1:1 water: ethanol and ethanol alone are compared over the same time period, the rate of return for beads cleaned with ethanol drops to 42%. The identification of beads most likely to have or develop glass deterioration and the long-term success of treatment will help prioritize conservation resources.