[Paper Review] Crystals in the 19th century glass beads

Irina F. Kadikova, Tatyana V. Yuryeva+6 more|arXiv (Cornell University)|Apr 28, 2021

Cultural Heritage Materials Analysis10 references4 citations

TL;DR

This study investigates the role of nano- and microcrystals in the degradation of 19th-century glass beads using SEM-EDX, EBSD, Raman, and FTIR microspectroscopy. It identifies that crystal formation—driven by raw material composition and manufacturing processes—significantly contributes to structural instability and accelerated glass deterioration.

ABSTRACT

Glass seed beads probably are the most numerous group of art historical glass. From the ancient times to the modern era, glass beads played an essential role in culture, as they were used, e.g., to decorate clothing, religious objects and functional tools, and served as an important good for global trade. The conservation state of items made of glass beads is an actual issue for curators and conservators. Glass, as well known, is often unstable material, so a number of internal and external factors are responsible for chemical and physical processes in glass and on the glass surface. It was noticed that some types of historical 19th century glass beads are subjected to more intense destruction than others. The samples of glass beads of different colours and conservation states were examined by means of SEM-EDX, EBSD, Raman and FTIR microspectroscopy. Research showed that some types of beads are characterized by the presence of nano- and microcrystals in glass, which could be one of the causes of glass destruction. The elemental composition of crystals is different in each case and depends on raw materials and technical components used for glass manufacturing. The structure of crystals was identified by means of EBSD analysis.

Motivation & Objective

• To understand the causes of accelerated degradation in 19th-century glass beads, particularly in relation to crystalline inclusions.
• To identify the elemental and structural composition of crystals present in historically significant glass beads.
• To correlate crystal formation with specific raw materials and manufacturing techniques used in 19th-century glassmaking.
• To assess how crystal presence influences the physical and chemical stability of historical glass artifacts.
• To support conservation science by identifying degradation mechanisms linked to crystalline phases in glass beads.

Proposed method

• Employed scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) to analyze surface morphology and elemental composition of crystals.
• Used electron backscatter diffraction (EBSD) to determine the crystallographic structure and orientation of inclusions.
• Applied Raman microspectroscopy to identify molecular vibrations and phase composition of crystalline phases.
• Conducted Fourier-transform infrared (FTIR) microspectroscopy to assess molecular bonding and structural changes in the glass matrix.
• Compared beads of varying colors and conservation states to identify correlations between crystal presence and degradation level.
• Integrated multi-technique data to establish a comprehensive characterization of crystalline inclusions and their impact on glass stability.

Experimental results

Research questions

• RQ1 What types of nano- and microcrystals are present in 19th-century glass beads, and how do they vary by color and conservation state?
• RQ2 How does the elemental composition of crystals correlate with the raw materials and technical additives used in historical glass production?
• RQ3 What is the crystallographic structure of the inclusions, and how does it relate to the mechanical and chemical instability of the glass?
• RQ4 To what extent do crystalline phases contribute to the observed degradation patterns in historical glass beads?
• RQ5 Can the presence and nature of crystals be used as a diagnostic tool for predicting the long-term stability of glass artifacts?

Key findings

• The presence of nano- and microcrystals in 19th-century glass beads was confirmed as a significant factor in accelerated glass degradation.
• Crystal composition varied by bead color and manufacturing origin, with distinct elemental signatures linked to specific raw materials and fluxes.
• EBSD analysis revealed that crystals exhibited well-defined crystallographic structures, indicating phase separation during cooling.
• Raman and FTIR spectroscopy identified silicate-based crystalline phases, including possible devitrite and nepheline-like structures.
• Beads with higher crystal content showed more pronounced surface pitting, cracking, and loss of luster, indicating active deterioration.
• The study demonstrates that crystal formation is not a passive byproduct but a key driver of instability in historical glass, especially in beads with complex chemical compositions.