Dyes derived from brazilwood (Caesalpinia spp.) are known to have been used in a diverse range of objects, from Medieval European textiles to North American First Nations objects, while pigments made from brazilwood feature in the palette of a number of painters, including Rembrandt and Van Gogh. For almost two decades, an unknown marker has been used to detect brazilwood colourants in historical objects. Limited sampling opportunities mean that the identification of the chemical structure of this marker has eluded scientists to date. Using a combination of synthesis, UPLC-ESI-MS/MS, HPLC, NMR and GC-MS, the identity of this unknown marker was confirmed as the benzochromenone, urolithin C. Structural identification provides a reliable reference compound for use across a range of analytical techniques employed in the cultural heritage sector and will enable the future development of non-destructive techniques for its identification on high-status objects.

The effect of visible radiation of different wavelengths on the deterioration of several fugitive artists' pigments and dyed textiles has been assessed. For red and yellow pigments, damage decreases as the wavelength increases. The relationship between wavelength and colour change for blue pigments and for ISO blue wool standards nos. 1-3 is less straightforward: radiation in the blue region is not necessarily the most damaging for these colorants. The deterioration caused by particular wavelengths depends on the energy of the radiation and the spectral absorbance properties of the colorant. The implications of the results on the selection of light sources and the use of blue wool standards to assess damage to museum collections are discussed.

Nine types of accelerated light‐ageing regimes, used by five institutions in the UK and one in the Netherlands, are described. Sets of nine painted paper and textile samples, including ISO Blue Wool Standards 1 and 2, were given the same nominal light exposure, then compared by means of colour measurements. Differences in colour change caused by different ageing methods are discussed in terms of the spectral power distribution of the light sources and the average temperature of ageing.

The oldest painting in the National Gallery collection, The Virgin and Child Enthroned by Margarito d’Arezzo (NG564), dated to about 1263–4, depicts the Virgin and Child in a mandorla, surrounded by scenes of the Nativity and lives of the saints, set within red and decorative black borders, against a gilded background. The materials and technique were investigated using a combination of non-invasive techniques, such as Fibre Optic Reflectance Spectroscopy (FORS) and macro X-ray fluorescence scanning (MA-XRF), and the analysis of a small number of paint samples using energy dispersive X-ray analysis in the scanning electron microscope (SEM-EDS), High-Performance Liquid Chromatography (HPLC), Attenuated Total Reflectance—Fourier transform infrared spectroscopy (ATR-FTIR) and micro X-ray Diffraction (micro-XRD). The results provided evidence for the use of a number of organic colourants, with both indigo and red lake pigments identified. The finding of an unusual compound, syngenite (K₂Ca(SO₄)₂·H₂O), is here postulated as a potential substrate for an organic yellow lake pigment. In addition, reference pigments were prepared to explore this hypothesis. Although documentary evidence confirms that yellow lakes were being produced from an early date, there is very little direct evidence for their use in 13th-century panel paintings.

During the fifteenth and sixteenth centuries, city guilds strictly regulated the quality of materials used to produce painted artefacts. The use of gold, ultramarine and other expensive materials was rigorously controlled, and stipulations were also made concerning the use of cheaper pigments. The Munich painters' guild ordinances of 1448 forbade the substitution of paris rot or rösel for lack, but was this for reasons of cost or some property of the pigments? From contemporary sources the authors believe that rösel was made from brazilwood, even then known to be impermanent. The recipes for Paris red suggest, however, that it could be made from several materials: brazilwood, lac or shearings of cloth dyed with madder or kermes, and the stability must have depended on which of these was used. Lack could also be prepared from a variety of materials, including shearings. The issue of what Paris red might be, and why the Munich guild legislated against it, was examined by investigating the lightfastn...