Raman microspectroscopy of blue‐green historical beads: Comparative study of undamaged and strongly degraded samples

Abstract

Confocal Raman microspectroscopy is used to substantially supplement existing experimental data on historical blue‐green beads with respect to the presence and distribution of potassium antimony silicate (KSS) crystals. Problem of degradation of blue‐green beads on historical artifacts accounts for topicality of the work. The reasons for possible short‐term (several years) degradation of beads and the presence of neighboring damaged and undamaged beads on a single item remain unknown in spite of multiple experimental works on various glasses. Presence of KSS microcrystals may serve as a reason for degradation of beads. Raman measurements at several depths are used to determine the distribution and estimate sizes of KSS microcrystals. Such distributions are different for undamaged and strongly degraded beads. For degraded beads, Raman data show the depth dependence of the concentration of (non)bridged oxygens in the near‐surface layer with a thickness of 3–4 μm (i.e., inhomogeneity of glass matrix). The results prove the growth of KSS microcrystals in historical blue‐green beads, which may cause internal stress and, hence, degradation. The results can be used for optimization of storage conditions and restoration procedures for historical items.

Glass depolymerization in the process of long-term corrosion: A study of deteriorating semiopaque turquoise glass beads using micro-FTIR spectroscopy

“…This result agrees well with the Raman spectroscopy data. The appearance of an intense line of Raman scattering peaked at 980 cm −1 [17], usually associated with the Si 2 -O 6 4 (Q 2 ) units, in the degraded turquoise bead glass evidences in support of the simplification of the glass structure in the course of its degradation and dominance of the silicate chain (Q 2 ) units in damaged glass.…”

“…Recently, we have presented our Raman study of the 19th century turquoise beads at different stages of degradation and demonstrated substantial changes of the glass structure at the late stages of corrosion, as well as its changes depending on depth in subsurface layers of a degraded glass grain [17]. Besides, we have determined for the first time the characteristic Raman bands of orthorhombic KSS [14,17]. 5 This paper presents the results of the Fourier-transform infrared (FTIR) spectroscopy study of historical turquoise glass beads.…”

Glass alteration in the process of long-term corrosion caused by internal stress: A comparative study of degraded and intact domains in 19th century semi-opaque turquoise glass seed beads using micro-FTIR spectroscopy and SEM

“…Raman spectra of the synthesized standard of orthorhombic KSbOSiO 4 are presented in Refs. [25,38,39]. Their characteristic feature is an intense narrow peak at about 532 cm −1 .…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XIII

“…Balakhnina and co‐workers used Raman microspectroscopy to compare undamaged and strongly degraded samples of blue‐green historical beads with respect to the presence and distribution of potassium antimony silicate crystals. Their results can be used for the optimization of storage conditions and restoration procedures for historical items . Peris‐Diaz et al employed Raman spectroscopy coupled to chemometrics to the discriminate provenance and geological age of amber.…”