Egyptian Blue samples

The chemical compositions of the ancient Egyptian Blue samples (reported in the following section) were determined by atomic absorption spectrophotometry using the hydrofluoric acid digestion method together with the lithium metaborate fusion method for the silica determination (9). Some 20-30 mg of powder drilled from the objects was used for these analyses. Additionally, the arsenic concentrations were determined by x-ray fluorescence spectrometry. The precision of the analytical data was 1-2% for the major elements (>10% concentration) and deteriorated to 5-20% for the trace elements (<0.1% concentrations). However, due to the inhomogeneity of the material, variations in elemental concentrations (i.e., major, minor, and trace) of 10-15% can be expected within a single object. 

Hardness measurements using the Mohs scratch test were undertaken on the complete range of ancient and laboratory-produced Egyptian Blue samples (Appendix B HAR and Table I, respectively). 

On the basis of direct visual comparison of the body, as opposed to the original surface, the ancient and laboratory-produced Egyptian Blue samples were grouped into three broad color categories dark blue, light blue, and diluted or pale light blue (Appendix B COL and Table I). 

Figure 4. Sample No. 14122 (Roman) high alkali, coarse texture, continuous, hardness >3 Mohs, dark blue. Thefollotcing phases can be identified Egyptian Blue (white), glass (light gray), and quartz (dark gray).

Figure 10. Sample No. 13714 (Nineveh) low alkali, fine texture, fragmented, hardness 1 Mohs, light blue. The following phases can be identified Egyptian Blue (white) and quartz (gray). No areas of glass are visible.

Also with the low-alkali mixtures, more Egyptian Blue crystals were produced when the samples were pelleted by using a screw press than when using hand pressure. 

---