Fig 1.
(A) Reflected visible light image of sample 2636. (B) Corresponding VIL image showing Egyptian blue is in the head dress. Egyptian blue standard is shown at the bottom of the images.
Table 1.
Multispectral imaging (presented as false color based on composite images in S1 Fig) and XRF results indicate the presence of luminescence and key elements associated with EB production.
Fig 2.
EDS analysis of a representative sample, 2526.
(A) Back-scattered electron (BSE) image. (B) All EDS data is plotted on a ternary diagram where yellow represents the highest density of points. The centroid and 3 standard deviations of the data are plotted in red. (C) The centroid of all EDS samples colored according to k-means cluster groups. (D) EDS data replotted as data clusters assigned by the Gaussian mixture method. (E) The pixels of the EDS map are recolored according to the cluster to which they belong, corresponding to the color scheme in (D). (F) The centroid of each Gaussian mixture cluster corresponding to pigment grains for each shabti sample, colored according to the groups identified using k-means clustering. The composition of cuprorivaite is marked by dashed lines in (B) and (D). In (C) and (F) the centroid of each group is represented with an “x”.
Fig 3.
Spectroscopic mapping of phases and luminescence.
(A) Schematic of the Raman and photoluminescence spectra acquired. (B) Component spectra identified in the Raman maps. (C) Spectrum of characteristic luminescence spectrum identified. (D) Optical image of sample 2526. (E) Phase and luminescence map of the area in (D). (F) Optical image of sample 2636. (G) Phase and luminescence map of the area in (F). (H) Optical image of sample 2601. (I) Phase and luminescence map of the area in (H). Phase and luminescence maps are colored according the Raman spectra in (B) and luminescence spectrum in (C).
Fig 4.
Analysis of Raman spectra for identified pigment phases.
The Si-O stretching region of the Raman spectra for (A) Egyptian blue and (B) the silicate glass phase is analyzed by fitting Gaussian curves to the original spectra (black). The total fit, including contributions from sulfate and carbonate vibrations (1010 and 1081 cm-1 respectively), is indicated by the red dotted line. The insets show the total area associated with Si-O vibrations and the relative contribution of the Q2 band.
Fig 5.
Correlative characterization of pigment samples from the two EDS groups.
(A) EDS map of sample 2526 showing the pigment grains have copper rich, calcium rich and silicon rich regions. (B) Clustered data from (A) (as in Fig 1E) shows that these regions cluster together. (C) Luminescence map acquired reveals that intensity varies within pigment grains. D) EDS map of sample 2601 shows more homogeneous pigment grains with some silicon rich regions and calcium rich binder. E) Clustering of the EDS data in (D) confirms the homogeneity of the pigment grains. F) Luminescence map acquired of the region indicated by the dashed line in (E) shows that intensity varies between grains but less so within the pigment grains.