Optical Coherence Tomography (OCT) for the Conservation and Interpretation of Faience
Vitreous materials are glass or glass-like substance. This project is focused on the study of ancient Egyptian faience. The main interest is related to the acquisition of information about the manufacturing techniques.
Ancient Egyptian faience is a non-clay ceramic material consisting of a fine- or coarse-grained silica (quartz) core, an alkali-lime glaze and, in most cases, an interaction layer connecting these layers. The manufacture of faience in Egypt dates back to the fourth millennium. Three methods for the production of ancient Egyptian faience have been identified:
Egyptian faience from the British Museum's collection, along with a schematic of the layers seen in Egyptian faience.
(i) application glazing in which a slurry is prepared either directly from a mixture of quartz, alkali flux, calcium carbonate and colorant and applied to the quartz body prior to drying and firing to about 950°C;
(ii) efflorescence glazing in which the glazing components are mixed with the quartz. Water is added, and objects are formed from the resulting paste. During subsequent drying, the soluble salts migrate to the surface to form a thin layer from which the glaze is produced after firing; and
(iii) cementation glazing (Qom technique) in which the quartz bodies are buried in the glazing mixture and fired to about 1000°C. After firing, the glazing mixture is broken away from the faience objects that are now coated with glaze.
Addressing the Challenge
Our early studies with the 930nm showed that OCT is useful for examining the cross-sections of the faience for studying the layers of the faience, however, the OCT could only examine the glaze and interaction layers. Recent studies with our in-house developed longer wavelength OCT at 1960nm produced cross-sections that could image all the way to the core of the faience. Investigations into the manufacturing techniques of Egyptian Faience objects can be done non-invasively, which also increases the scope and collections of objects that can be examined.
(a) Colour image of an Egyptian faience from the British Museum collection (© BM); (b) Scanning electron microscope (SEM) image of a cross-section, showing all the three layers of the faience structure; (c) virtual cross-section obtained by 930 nm OCT reveals the two top layers of the faience body; (d) virtual cross-section obtained using 1960 nm OCT shows all the three layers of the faience body.
A pilot OCT survey of Egyptian Faience at the BM has been conducted.
Preliminary results were presented at the LACONA 12 conference in Paris, France http://lacona12.org/
Read, M., Cheung, C.S., Liang, H., Meek, A. and Korenberg, C. 2021. A Non-Invasive Investigation of Egyptian Faience Using Long Wavelength Optical Coherence Tomography (OCT) at 2µm. Studies in Conservation Doi: 10.1080/00393630.2020.1871208
Liang, H., Sax, M., Saunders, D. and Tite, M., 2012. Optical Coherence Tomography for the Non-Invasive Investigation of the Microstructure of Ancient Egyptian Faience. Journal of Archaeological Science, 39, pp. 3683-3690.
Dr Fouzia Ouali (Nottingham Trent University)
Dr Capucine Korenberg (The British Museum)
Dr Andrew Meek (The British Museum)
Margaret Read (Nottingham Trent University)
AHRC Collaborative Doctoral Award
The British Museum