P. Mirti et al., A STUDY OF ROMAN GLASS BY REFLECTANCE AND ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPIES, Spectrochimica acta. Part A: Molecular spectroscopy, 49(9), 1993, pp. 1361-1371
Reflectance and electron paramagnetic resonance (EPR) spectroscopies w
ere used to study 25 fragments of Roman glass. Colour coordinates were
used for an unbiased classification of the glasses in colour groups,
which accounted for the presence of blue, blue-green, green, yellow-gr
een, yellow and purple samples. Reflectance spectra were recorded in t
he 250-2500 nm wavelength range and showed absorption bands characteri
stic of Fe(II), Fe(III) and Mn(III) ions; furthermore, Co(II) and Cu(I
I) bands were observed in the spectra of the blue glasses. A decrease
of the absorbance ratio of Fe(II) to Fe(III) ions was observed moving
from blue-green to green and yellow-green glasses; however, yellow fra
gments still proved to be reduced glasses. EPR spectra displayed the c
haracteristic patterns of Fe(III) and Mn(II) ions, with g-values in th
e 2-5 interval and spectral features depending on the relative content
of the two elements. The characteristic pattern of the V(IV) ion (g a
lmost-equal-to 2) and signals due to the formation of iron-sulphur com
plexes (g almost-equal-to 6) appeared in the spectrum of a dark yellow
glass, recorded at 77 K.