Spectroscopic Studies on the Darkening of Lead White

Lead white is an historically important paint used by artists since antiquity. The darkening of lead white has been well documented in works of art such as paintings. In this paper, mid-infrared (MIR) and visible spectroscopy were used to examine spectral changes accompanying the darkening of lead w...

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Bibliographic Details
Published in:Applied spectroscopy 2003-11, Vol.57 (11), p.1393-1398
Main Authors: Goltz, Douglas, McClelland, Jennifer, Schellenberg, Angela, Attas, Michael, Cloutis, Edward, Collins, Cathy
Format: Article
Language:English
Subjects:
Color
Colorimetry - instrumentation
Colorimetry - methods
Hydrogen Sulfide - analysis
Hydrogen Sulfide - chemistry
Lead - analysis
Lead - chemistry
Paint - analysis
Spectroscopy, Fourier Transform Infrared - methods
Spectrum Analysis - methods
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Summary:Lead white is an historically important paint used by artists since antiquity. The darkening of lead white has been well documented in works of art such as paintings. In this paper, mid-infrared (MIR) and visible spectroscopy were used to examine spectral changes accompanying the darkening of lead white paint as a result of exposure to H2S(g). Laboratory-prepared paint and a commercial lead white paint were used to observe the darkening reaction overtime. Structural changes to the pigment, 2PbCO3Pb(OH)2, in lead white were readily detected using MIR by applying a thin film on a KBr pellet. Spectral changes at 3541 (O–H stretch), 1400 (C–O), and 680 cm−1 (C–O) were the most significant over time as the paint darkened. Visible spectra were also collected to provide a semi-quantitative measure of color change with structural changes observed by MIR. Experiments in the visible region were also conducted to compare the spectral response as % reflected and % transmitted light as lead white darkened. The effect of different binding agents (egg tempera, linseed oil, water, and gum Arabic) on the rate of darkening of lead white was also examined. Other sulfur-containing pigments such as orpiment and realgar were also tested for their ability to darken lead white. By applying paint as a thin film inside a sealed cuvette, darkening of lead white was observed in the visible spectra (800 nm) when either powdered orpiment or realgar was in placed in the cuvette for 24 h.
ISSN:0003-7028
1943-3530
DOI:10.1366/000370203322554563