THE ORIGIN,DESTRUCTION AND RESTORATION OF COLOUR IN EGYPTIAN TRAVERTINE*

Travertine was one of ancient Egypt's most popular ornamental stones. Upon prolonged exposure to sunlight, the rock's translucent brownish calcite is bleached to nearly white. Ultraviolet and gamma irradiation experiments were undertaken to investigate the source of the brownish colour and the process by which it fades. It was found that the coloration results from the activation of colour centres by natural radioactivity within the rock, and that these colour centres are deactivated by the ultraviolet component of sunlight. The results also demonstrate that the original brownish colour of sun‐bleached, travertine objects can be restored by artificial gamma irradiation.     

DETECTION OF ANCIENT MARBLE FORGERY: TECHNIQUES AND LIMITATIONS*

Since 1960, scientific results have replaced aesthetic judgements in marble authentication studies and the technology to perform analytical tests on micro‐samples has developed rapidly. However, no single method can be used to determine the authenticity of a piece of marble. A ‘detective‐like’ investigation is usually adopted by using optical microscopy, ultraviolet‐induced fluorescence, provenance determination techniques and mineralogical, chemical and morphological analyses of the patina. A newly proposed thermoluminescence methodology calculates the ‘burial age’ of recently excavated objects or distinguishes artefacts exposed to sunlight since antiquity from those exposed recently. The technique shows a lot of potential; however, much work remains to be done.