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

Abstract

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.

Raman investigation of the structural changes during alteration of historic glasses by organic pollutants

“…These bands and, in particular, the sharp band at 990 cm 1 are present in the original glass spectra and are thought to be associated with the presence of lead. 29 This hypothesis is supported by the elemental analyses, which indicate that lead ions remain in the altered glass structure. Consequently, lead ions and the silicate species to which these are coordinated (giving the sharp band around 990 cm 1 ) were not affected by alteration and so retain their place in the structure.…”

“…23 It is interesting to note that the cation content remaining in the altered structure is much higher in the Islamic glass than in the British glass, probably because of differences in the stabiliser ion content in the original composition. As a consequence, the band around 550 cm 1 (B550), whose wavenumber depends on the cation content, 29 is still present in the spectrum of the altered Islamic glass, although shifted to the lower wavenumber of 548 from 573 cm 1 , but is absent in the altered British glass.…”

“…29 In the present investigation the modification of the structure following alteration is examined for two 19th century objects from the NMS collections: a British decanter (unregistered) and an Islamic bottle (museum reference A.1893.61). The two objects were chosen because their base composition is similar as both are silicate glasses with major soda content but differ in the stabiliser cation content.…”

“…Since both the glasses examined had a soda-silicate composition, the decomposition was based on the model defined previously for alkali glasses. 29 The same model was applied to both altered and unaltered glass spectra to allow comparison. The model provides an objective basis for describing and quantifying the changes in the complex lineshapes that we observe.…”

KSbOSiO4 microcrystallites as a source of corrosion of blue-green lead-potassium glass beads of the 19th century

“…The process of deterioration of the glass beads have usually been associated by researchers with the impact of external factors on the glass, especially atmospheric moisture and / or a cloth or a leather on which the beads were sewn, 12 resulting in so called crizzling, 17 a specific roughening or cracking of the glass surface. 18,19,20,21 Such corrosion flows in several stages: the moisture comes into contact with the surface of the glass, the glass leaches, forms a near-surface layer depleted in alkali metals, this layer cracks, moisture penetrates deeper, cracking process increases, and the glass breaks into fragments. However, this scenario contradicts the fact that similar beads at different phases of deterioration-intact, slightly cracked, severely cracked and changed the color or discolored, partially or completely fragmented-are often present on a single exhibit in immediate neighbourhood (Figs.…”