A Non-invasive Investigation of Egyptian Faience Using Long Wavelength Optical Coherence Tomography (OCT) at 2 mu m

Egyptian faience is a non-clay ceramic semi-transparent material formed of a quartz core and alkali-lime glaze. Previous investigations have identified production techniques by using microstructure images obtained from invasive methods. Optical coherence tomography (OCT) is a non-invasive 3D imaging technique that produces virtual cross-sections of transparent and semi-transparent materials. A previous study by one of the authors demonstrated the feasibility of non-invasive investigation of microstructures of Egyptian faience using 930 nm OCT, but the limited probing depth prevented viewing down to the quartz core of the objects. This paper shows that an in-house developed OCT system using a longer wavelength (2 mu m) was able to image the full microstructure from the top glaze layer down to the core, allowing rapid and non-invasive studies of intact objects and demonstrating the potential for surveying large museum collections. OCT virtual cross-section images at 5 wavelengths, 550, 810, 930, 1300 and 1960nm, were compared and the optimum wavelength for OCT investigation of Egyptian faience microstructure was found to be 2 mu m.