AIC's 42nd Annual Meeting

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. Glass disease is a collection wide condition issue at the National Museum of the American Indian. Two targeted collections surveys, has identified 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 fourteen years. A second survey was conducted to evaluate whether treatment options used for blue and red beads – cleaning with water, ethanol 1:1 water:ethanol, or mechanical cleaning – had different long term results. Red and blue beads with records of deterioration were chosen to create a relevant subset and because the previous condition change survey had identified those colors as most likely to deteriorate. The results of both surveys will be presented, including trends indicating which beads were most likely to develop glass disease. Several factors stood out, including color and manufacturing technique, both of which are directly related to glass composition. Wound beads – as opposed to drawn beads – also had much higher rates of deterioration, likely due to the generally lower concentration of stabilizing calcium oxide (CaO) and the use of potash (K2CO3) as the alkali constituent. Additional information about the bead compositions will be gathered through x-ray fluorescence spectroscopy. The identification of beads most likely to have or develop glass deterioration and the long term success of treatment will help prioritize conservation resources.