Near infrared reflectography for deciphering obscured (whitewashed or ablated) epigraphs

Abstract

Infrared reflectography (IRR) is a non-destructive imaging technique based on the different optical behaviour of visible and near infrared (NIR) radiation through a thin pictorial layer. This effect is a consequence of both lower NIR absorption and reduced NIR scattering due to the particle size smaller than the wavelength. Here we present an interesting and, to our knowledge, new application of this technique to ancient multi-layered epigraphs, showing its useful application in archaeology. Both tests on laboratory samples and preliminary tests on the field show that it is possible to use IRR taken with a vidicon wide spectral range camera (let us call this NIR reflectography (NIRR) to underline the wide spectral range including almost all NIR, but excluding thermal infrared radiation), to read inscriptions ‘deleted’ by means of a whitewashing layer. The field tests carried out on a multi-layer inscription ‘notice board’ in Herculaneum have shown that NIRR can also be useful in integrating some gaps of the currently visible layer inscription and in reconstructing the layout of the inscription wiped off by mechanical abrasion. All these applications are of much interest since ancient Greek and Latin public documents were frequently written with black pigment on whitewashed boards and ‘wiped off’ when the inscription was no more required.