Warm white LED lighting in museums: Ageing effects on terpenoid resins assessed through Raman spectroscopy and chemometrics

In this work, warm white (3,000K) LEDs were used for investigating accelerated ageing of different classes of natural terpenoid compounds. In particular, colophony, sandarac, shellac, and mastic resins were considered. Maximum total irradiance of 80Mlxh was used, which can be compared to about 130years of exposure in recommended museum conditions. Moreover, another set of the same resins was kept in darkness conditions in order to assess kinetic differences. Raman spectroscopy was employed to assess molecular changes occurring in resins structures during both dark and light ageing. Spectroscopic information was achieved through a portable Raman scanner provided with a narrow-band CW diode-pumped Nd:YAG (1,064nm) laser and an NIR spectrometer equipped with an InGaAs linear array. Vis-LED light appears to be suitable to avoid yellowing in the case of mastic and colophony resins suggesting that it is advisable to use this light with respect to traditional halogen lamps for illuminating museums and art galleries. Conversely, the ageing process of sandarac and shellac appears not to be particularly affected by the UV radiation. Raman spectroscopy in combination with multivariate analysis (principal component analysis) was able to provide information about the ageing process of colophony both in light and dark conditions.