Visual degradation in Leonardo da Vinci's iconic self-portrait: A nanoscale study

Abstract

The discoloration of ancient paper, due to the development of oxidized groups acting as chromophores in its chief component, cellulose, is responsible for severe visual degradation in ancient artifacts. By adopting a non-destructive approach based on the combination of optical reflectance measurements and time-dependent density functional theory ab-initio calculations, we describe and quantify the chromophores affecting Leonardo da Vinci's iconic self-portrait. Their relative concentrations are very similar to those measured in modern and ancient samples aged in humid environments. This analysis quantifies the present level of optical degradation of the Leonardo da Vinci's self-portrait which, compared with future measurements, will assess its degradation rate. This is a fundamental information in order to plan appropriate conservation strategies. (C) 2014 AIP Publishing LLC

Recognizing ancient papyri by a combination of spectroscopic, diffractional and chromatographic analytical tools

“…These can be measured by classic titrational methods8 or by FTIR and UV/Vis spectroscopic methods as presented by us before1027.…”

Quantitative diagnostics of ancient paper using THz time-domain spectroscopy

“…In fact, the increasing degradation of paper indicated by the crystallinity has as consequence the consumption of the amorphous regions with a consequent decreasing of the density of H bonds (C). The increasing oxidation of samples [13,24] causes the lost of the hydrophilic character of the accessible regions due to the progressive transformation of hydroxyl groups into carbonylic groups (A).…”

“…The values of v for the samples studied are reported in Table 2. Such numbers are required to calculate the absolute absorption coefficient (α) of cellulose fibers, given that THz radiation probes the volume averaged properties of the papers sheets [27,24,28,20]:…”

“…Cellulose was modeled as a crystal in its most common crystalline form (I β phase), as in Refs. [24,27,28]. Both the unit cell and the atomic coordinates of the structures were relaxed by using a densityfunctional-theory plane-wave code with ultrasoft pseudopotentials (QUANTUM ESPRESSO [33]).…”

“…Proper ultrasoft pseudopotentials [38], conveniently generated [39] to be suitable for the nonlocal VdW functionals, were used. The Irreducible Brillouin Zone has been sampled with 14 k-points [24,27,28]. Vibrational properties have been calculated using finite displacements within the DFT framework, as described in Ref.…”