The use of Raman spectrometry to predict the stability of historic glasses

In the National Museums of Scotland (NMS) widespread alterations have been observed in the glass collections of 19th to 20th century, affecting British, Islamic and Asian glasses. It is important for museums to be able to distinguish between stable and unstable glasses, so that particular care can be taken to preserve the most sensitive objects. Elemental analysis by electron microprobe of a selection of stable and unstable British and Islamic glasses indicated that the composition was directly linked to the degree of stability of the glass. Because sampling of glass objects is often difficult or impossible, we investigated the ability of Raman spectroscopy, which can be applied in situ and non‐destructively, to distinguish between stable and unstable glasses. The analysis concentrated on the soda‐lime silicate glasses, which displayed a mixed stability. We show, by combining the elemental composition and the Raman spectroscopy data, that a correlation can be established between the 550 cm −1 band shift and the SiO 2 content (or degree of polymerisation). A second correlation was established between the 950 cm −1 band and the number of cations charge‐coordinated to the silicate with two non‐bridging oxygens (NBOs). Finally, a method based on the peak area ratio ( A 900 + A 950 + A 990 )/( A 900–1150 ) from the Raman spectrum is proposed to determine the stability of soda silicate glass.