Colour modifications and hyperspectral imaging: non-invasive analysis of photo-degraded wood surfaces

Abstract

The aim of this investigation is to study the changes occurring on the surface of poplar wood exposed to solar irradiation, in a controlled environment. Poplar is poor of coloured extractive, so that the surface changes are attributed to the main wood constituents’ modifications and the contribution of extraneous substances to holocellulose and lignin can be considered negligible. The poplar wood samples were irradiated in a Solar Box chamber, equipped with a 280 nm UV filter, until reaching 504 hours. The colour changes were monitored with the reflectance spectrophotometer of X-Rite CA22 according to the CIELAB system. The surface chemical modifications were evaluated by measuring the infrared spectra with a Fourier Transform Infrared spectrometer (FT-IR) operating in DRIFT modality. Hyperspectral imaging (HSI) was also applied to study the surface wood changes by using a SisuCHEMA XL Workstation operating in the SWIR range (1000-2500 nm). The data obtained from the different techniques applied were put in comparison in order to find possible correlations between them also with the aim to evaluate the applicability of the HSI technique to the investigation of wood modifications, in a totally non-invasive modality. The possibility to find a correlation between colour changes and chemical modifications, investigated both with traditional and innovative methodologies, in wood surfaces can have practical application in cultural heritage and contemporary objects.