Shuya Wei

UV ageing studies: evaluation of lightfastness declarations of commercial acrylic paints

The lightfastness declarations of several different commercial acrylic paints and different quality series were tested by artificial UV ageing. To evaluate their lightfastness declarations, three acrylic colours (cadmium red, ultramarine blue and chromium oxide green) from six companies (Lascaux, Liquitex, Lukas, Rembrandt, Schmincke, and Winsor & Newton) were analysed before and after UV exposure. Characterisation and identification of these materials were carried out with Py–GC/MS, FTIR–ATR analyses, and colour measurements. Particular attention was focused on the Py–GC/MS measurements and on comparison of the single-shot method for pyrolysis of polymers and the double-shot mode which enables a unique combination of pyrolysis methods for analysis of polymers and thermal desorption for documentation of the volatile compounds. Depending on the particular company and the specific value of the lightfastness declaration, different binding media (i.e. poly(EA/MMA), poly(nBA/MMA), and poly(2-EHA/MMA)), and fillers (i.e. kaolinite, calcium carbonate, barite, and talc) were characterised and identified by Py–GC/MS and FTIR–ATR analyses. After UV exposure, several alteration processes with consequent formation of volatile compounds or new products were observed by both techniques, especially for the blue paints. In particular, the double-shot mode of Py–GC/MS enabled the detection of oxidation products, which could not be detected with the single-shot mode. Comparison of the lightfastness declarations for each of the blue, green, and red paints and the noted alterations broadly agreed for most of the paints.

Thermal analysis of the interaction of inorganic pigments with p(nBA/MMA) acrylic emulsion before and after UV ageing

Differential scanning calorimetry (DSC) and thermogravimetry (TG) analyses were used to investigate the influence of inorganic pigments on the photo-oxidative stability of an acrylic emulsion binding medium. For this purpose, three different types of inorganic pigments such as ultramarine blue, cadmium red and hydrated chromium oxide green were selected and mixed with an acrylic emulsion binding medium of poly(n-butyl acrylate/methyl methacrylate). These laboratory mixed paints were analysed before and after UV exposure for different periods of time. In addition, three acrylic commercial paints such as ultramarine blue, cadmium red and chromium oxide green from Liquitex® and Rembrandt® companies were also analysed. The results obtained with both thermal techniques suggested that ultramarine blue has the strongest influence on the photo-oxidative stability of the binding medium. A higher increase of the glass transition temperature Tg was observed by DSC analysis on the UV aged binder mixed with ultramarine blue. This result was confirmed by the TG investigations that showed a gradual decrease of the initial temperature of degradation as well as the strongest decrease of the final mass% of the organic compounds. Similar results were measured from the Liquitex® and Rembrandt® blue paints.

Analysis and identification of dyestuffs in historic Chinese textiles

Historical plant-based dyes are mainly blue, red, and yellow in colour, and are chemically classified as indigoids (blue), anthraquinones (red), and flavonoids (yellow). The main indigoid dyes are indigo and Tyrian purple. Plant indigo exists as the glycoside form and in China the colouring agent is mainly extracted from Persicaria tinctoria, also known as Polygonum tinctorium. By soaking the plant stem in water, the indigotin is obtained after fermentation, hydrolysis, and oxidisation [1]. The sources of the anthraquinone dyes are plants or insects such as madder roots, saffron, cochineal, and lac, etc. The origin of the dyes can be identified by the ratios of the anthraquinones [2]. Natural yellow dyes are mainly flavonoids or substituted hydroxy methoxy flavonols. Flavonoids can be used directly to dye cotton, wool, and silk to obtain a vivid yellow colour, while with a copper mordant (blue vitriol) they can give a green colour. The sources of natural yellow dyes are mainly weld (Reseda luteola L.), buckthorn berries (of the genus Rhamnus), Sophora japonica L., Rheum palmatum L., and Coptis root, etc. The various analytical methods used for the characterisation of dyestuffs include Fourier transform infrared spectroscopy [3], high-performance liquid chromatography (HPLC) often equipped with a diode-array detector in the ultraviolet region [4], and mass spectrometry. This study applied HPLC with time-of-flight mass spectrometry, with the aim of making a breakthrough in identifying organic dyes and understanding their degradation mechanisms: it mainly focuses on dyestuffs found on excavated 古代使用的主要植物染料有藍、紅、黃等顏色,按

A Study of the Materials Used for the Inscriptions on Ceramic Vessels

The Xiao Shuang Qiao site is located west of the city of Zhengzhou, Henan Province, China, and was excavated during the last few years. According to radiocarbon dating, the site dates back to the Middle Shang period (1400 BC). It represents another urban centre of the Shang Dynasty, perhaps the “AO” capital of Zhong Ding, King of Shang. Its discovery is extremely important for Chinese archaeology, covering a previously unknown period of the Shang Dynasty. At this site, apart from the great findings, such as a high platform foundation of a palace formed of rammed earth, dwellings, sacrificial pit clusters, ditches, refuse pits, and metal craft remains, a number of pottery ritual vessels with inscriptions written on them were also excavated. These written characters are from an earlier period than the oracle bone inscriptions of Shang and the bronze inscriptions of Shang and Zhou (Song 1996). They are of great significance not only in terms of the interpretation of the artefacts from this particular site, but also for the study of the origin and changes in ancient Chinese writing.