Multi-technique analysis of an ancient stratified glass eye
bead by OCT, μ-XRF, and μ-Raman spectroscopy
Junqing Dong (董俊卿)
1,2
, Qinghui Li (李青会)
1,2,
*, and Yongqing Hu (胡永庆)
3
1
Sci-Tech Archaeology Center, Laboratory of Micro-Nano Optoelectronic Materials and Devices, Key Laboratory
of Materials for High-Power Laser, Shanghai Institute of Optics and Fine Mechanics,
Chinese Academy of Scien ces, Shanghai 201800, China
2
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences,
Beijing 100049, China
3
Henan Provincial Institute of Cultural Relics and Archaeology, Zhengzhou 450000, China
*Corresponding author: qinghuil@sina.com
Received February 8, 2020; accepted May 15, 2020; posted online July 20, 2020
In this Letter, we report a combination of non-invasive analysis of the cross-section structure, phase, and chemi-
cal composition combining optical coherence tomography (OCT) with spectroscopic methods such as X-ray
analytical microscope (μ-XRF) and micro-Raman spectroscopy (μ-RS), which allow us to effectively and con-
veniently identify the colorants used for each color region and the glass-making process of an ancient multicol-
ored stratified glass eye bead. The results reveal that the sophisticated colors of the glass bead arise from the
transition metals and chemical compound crystals deliberately added in the same base glass and carefully ad-
justed by the glass maker to obtain four colors. We also propose and discuss the provenance of the glass bead.
It was probably introduced to China through the Northern Silk Road from Egypt or the Eastern Mediterranean
areas about 1400 years ago. The combined multi-analytical technique is the promising approach for precious
cultural heritage research.
Keywords: multi-spectroscopic methods; combination of non-invasive analysis; ancient stratified glass;
cross-section structure; chemical composition; glass-making process.
doi: 10.3788/COL202018.090001.
Some of the optical and spectroscopic techniques that
were initially developed for the fields of chemistry, biol-
ogy, biomedicine, materials sciences, and geology are used
as important methods to characterize the micro-structure,
elemental composition, coloring and opacifying agents,
and secondary phases of archaeological materials. The
common techniques are optical microscopy, optical co-
herence tomography (OCT)
[1,2]
, synchrotron radiation
micro-computed tomography (SR-μCT)
[3]
, laser ablation
inductively coupled plasma atomic emission spectrometry
or mass spectrometry (LA-ICP-AES/MS)
[4]
, s canning
electron microscopy coupled with an X-ray energy disper-
sive spectrometer (SEM-EDS)
[5]
, proton induced X-ray
emission (PIXE)
[6]
, micro-Raman spectroscopy (μ-RS)
[7]
,
X-ray fluorescence spectrometry (XRF)
[8]
, X-ray analyti-
cal microscopy (μ-XRF)
[9]
, and so on. Constrained by the
effects of the shape or uneven surface of samples and lim-
itations of the instrument itself, the information obtained
by a single technique is insufficient, while the combination
of multiple techniques is beneficial to realizing mutual
complementation and verification. In recent years, these
analytical instrum ents have been increasingly widely ap-
plied in research on biomedicine
[1,9–11]
and cultural heritage
(i.e., ceram ic
[2,12]
, porcelain
[13,14]
, potsherd
[15,16]
, glass
[3,8]
,
polychrome sculpture
[17]
, and amalgam mirror
[18]
).
As a non-contact method, OCT technology can
quickly and conveniently generate high-resolution cross-
sectional and three-dimensional images of the subsurface
of transparent and translucent materials. μ-XRF is a non-
destructive technique for simultaneous qualitative and
quantitative analyses of chemical components of points,
lines, and areas. μ-RS can obtain information on both mi-
croscopic morphology and the phase at the same time; es-
pecially, for ancient material, it can also identify pigments
and opacifiers, as well as provide further information on
the type of glassy matrix. For instance, Colomban and
coworkers have analyzed great quantities of archaeologi-
cal glasses and glazed ceramics by means of Raman spec-
troscopy (RS)
[7,19–21]
.
The eye bead (Fig.
1), as a popular ornament in ancient
time, first appeared in the 18th Dynasty of ancient Egypt
(1550 B.C.–1307 B.C.)
[22]
and was soon prevalent in North
Africa, Western Asia, and Southern Europe. Eye beads
originated from the eye of ancient Egyptian god statues,
most of which were inlaid with glass or gemstones in the
shape of eyes. The eye bead was considered a protection
against evil spirits by ancient Egyptians. Western Asians
thought that the god eyes with incomparable power can
drive away ghosts and evil spirits and bring safety
[23]
.
During the Spring and Autumn Period and Warring
States Period (about mid-eighth century B.C. to mid-fifth
century B.C.), glass eye beads were introduced gradually
to the Xinjiang, Inner Mongolia, Gansu, Shaanxi, Shanxi,
Henan, Hubei, Hunan, Chongqing, and Anhui Provinces
through the Silk Road
[24–27]
and were considered to be
significant evidences of cultural and economic exchanges
COL 18(9), 090001(2020) CHINESE OPTICS LETTERS September 2020
1671-7694/2020/090001(7) 090001-1 © 2020 Chinese Optics Letters