The development of a totally non-destructive methodology using fiber optic reflectance spectroscopy (FORS) in the visible and near-infrared region has been discussed by the authors in previous works. In the present communication, such a methodology was used to collect and compare spectra of several red lakes layered as pigments on wooden panels according to the treatises on materials that reflect medieval practice (tempera medium and gypsum ÷ glue mixture ground). There were two equivalent panels prepared : the first was stored in a box without any external light influence, while the second one was exposed to several cycles of UV light and then placed in open air sheltered from dust. The study of the colour change concerning painted lakes can provide important information on the fading process. A set of measurements was collected on both panels in order to determine the colour difference ?E. ?E was calculated starting from chromaticity coordinates according to the 1931 CIE recommendations and for a standard illuminant D65. The shift of the dominant wavelength due to the fading process has been computed for each of the lakes investigated. The study of the correlations between ageing and fading processes could be a useful starting point for setting several matter÷ compatible preservatives.
Colour analysis of historical red lakes using non-destructive reflectance spectroscopy
Bacci M;Orlando A;Picollo M;
1994
Abstract
The development of a totally non-destructive methodology using fiber optic reflectance spectroscopy (FORS) in the visible and near-infrared region has been discussed by the authors in previous works. In the present communication, such a methodology was used to collect and compare spectra of several red lakes layered as pigments on wooden panels according to the treatises on materials that reflect medieval practice (tempera medium and gypsum ÷ glue mixture ground). There were two equivalent panels prepared : the first was stored in a box without any external light influence, while the second one was exposed to several cycles of UV light and then placed in open air sheltered from dust. The study of the colour change concerning painted lakes can provide important information on the fading process. A set of measurements was collected on both panels in order to determine the colour difference ?E. ?E was calculated starting from chromaticity coordinates according to the 1931 CIE recommendations and for a standard illuminant D65. The shift of the dominant wavelength due to the fading process has been computed for each of the lakes investigated. The study of the correlations between ageing and fading processes could be a useful starting point for setting several matter÷ compatible preservatives.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
