Spectral Behavior of White Pigment Mixtures Using Reflectance, Ultraviolet—Fluorescence Spectroscopy, and Multispectral Imaging

Abstract

Reflectance spectroscopy, ultraviolet (UV)-fluorescence spectroscopy, and multispectral imaging have been widely employed for pigment identification on paintings. From ancient times to the present, lead white, zinc white, and titanium white have been the most important white pigments used for paintings and they are used as pigment markers for dating a work of art. The spectral behavior of these pigments is reported in several scientific papers and websites, but those of their mixtures are quite unknown. We present a combined nondestructive approach for identifying mixtures of lead white, zinc white, and titanium white as powder and dispersed in two different binder media (egg yolk and linseed oil) by using reflectance spectroscopy, spectrofluorimetry, multispectral reflectance and UV-fluorescence imaging. We propose a novel approach for mapping the presence of white pigments in paintings by false color images obtained from multispectral reflectance and UV-fluorescence images. We found that the presence of lead white mixed with either zinc white or titanium white is highly detectable. Zinc white mixed with lead white or titanium white can be identified due to its UV-fluorescence emission, whereas titanium white in association with lead white or zinc white is distinguishable by its reflectance spectral features. In most cases, the UV-fluorescence analyses also permit the recognition of the binder media in which the pigments are dispersed.

Characterization of spray paints used in street art graffiti by a non‐destructive multi‐analytical approach

“…Similar results have been obtained in previous studies, 4,9 in which titanium dioxide in the rutile crystal form was identified as one of the major components in various spray paints and street art graffiti samples. The use of titanium white is confirmed by the registered reflectance spectra for the white and light shades (Figure 1A) that show a characteristic steep rise with an inflection point around 410 nm 20 . Within the FTIR data, the presence of titanium white can be inferred based on the broad absorption in the lower wavenumber range 4 (750‐400 cm −1 ).…”

“…The use of titanium white is confirmed by the registered reflectance spectra for the white and light shades ( Figure 1A) that show a characteristic steep rise with an inflection point around 410 nm. 20 Within the FTIR data, the presence of titanium white can be inferred based on the broad absorption in the lower wavenumber range 4 (750-400 cm −1 ).…”

“…Characterization of the main binder as well as complementary information on the existing organic and inorganic pigments was carried by means of attenuated total reflectance (ATR) FTIR spectroscopy 4,15 . Spectrophotometry was used to obtain additional information on pigments in the visible range, 20 while HSI data coupled with chemometric techniques was used to extend the spectral characterization of the investigated materials in the SWIR wavelength range 21,22 . Compared to previous studies carried on street art graffiti materials, the present article proposes in addition to well established spectroscopic techniques, the use of hyperspectral imaging ‐ a promising non‐invasive methodology recently introduced for the remote identification and mapping of pigments 21 .…”

Post-Processing of VIS, NIR, and SWIR Multispectral Images of Paintings. New Discovery on the The Drunkenness of Noah, Painted by Andrea Sacchi, Stored at Palazzo Chigi (Ariccia, Rome)

“…This approach is very useful to recognize pigments which have large differences in the IR absorbance, although they appear similar to the eye (i.e., lapis lazuli shows a red false-color with respect to the much less expensive azurite that looks blue [20]). However, since any combination of three different images (not mandatorily corresponding to the ones just mentioned) could be defined as "False-color image", new perspectives are open to image processing, not necessarily involving IR range but aiming to underline different spectral features even in the visible range [21].…”

Characterization and Digital Restauration of XIV-XV Centuries Written Parchments by Means of Nondestructive Techniques: Three Case Studies

“…In the last 15 years, hyperspectral and multispectral imaging technique has been widely used for the imaging of fine art paintings [17,20] and ancient documents, aiming at the analysis of the materials used [21,22] and the digital restoration of degraded or erased parts [23]. Hyperspectral and multispectral imaging has been developed by combining both digital imaging and spectroscopy.…”