Analytical characterization of diterpenoid resins present in pictorial varnishes using pyrolysis-gas chromatography-mass spectrometry with on line trimethylsilylation

A procedure based on the technique of the pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) has been applied, in this work, in order to determine the composition of diterpenoid resin employed in art works. The method is based on the on line derivatization of these resins using hexamethyldisilazane (HMDS). Results obtained were compared with those previously reported in literature from Venice turpentine, Strasbourg turpentine, colophony, sandarac and Manila copal using this same method and with those others from in situ thermally assisted hydrolysis and methylation with tetramethylammonium hydroxide (TMAH). Canada balsam, copper resinate and Copaiba balsam have been also analyzed extending the scope of this method in the field of the analysis of artwork materials. Several non-reported trimethylsilylated derivatives of compounds present in the diterpenoid resins have been identified. An improvement in sensitivity has been obtained by using HMDS as derivatizing reagent, together with a better resolution of the most representative peaks. Additionally, this method reduces the number of pyrolytic fragmentation, recombination, dehydration and isomerization products formed during the pyrolysis process and, in consequence, more simplified chromatograms are obtained. Finally, the reported procedure has been successfully used for characterizing two diterpenoid resin-based varnishes present in the canvas painting "The Betrothal of the Virgin" (Anonymous, 17th century) which is included in the pictorial collection of Saint Joseph Church in Taormina (Italy) and the Magdalena Tryptich (Master of Alzira, 16th century, Valencia, Spain).     

Toward a Raman/FORS discrimination between Art Nouveau and contemporary stained glasses from CdSxSe1 − x nanoparticles signatures

CdS_xSe_{1 − x} quantum dots received considerable attention in academic studies and as cut‐off filters and indirect‐gap semiconductors. These later compounds have also been used for artistic purposes to produce colored glass since the 1920s thanks to their bright colors. Because non‐invasive conditions are now mandatory when considering objects belonging to the cultural heritage, the use of Raman and fiber optics reflectance spectroscopy has been identified as potential ones to obtain information about the nanostructure of six samples of historical glass produced between the late 1920s and modern days. The average elemental composition of the nanocrystals has been deduced processing both optical and vibrational data, and the result arising has been compared taking into account the several factors affecting the experimental results. The diffusion of zinc inside the nanocrystals has also been questioned by the shift caused on the CdS‐ and CdSe‐like phonon band wavenumber and on the absorption edge wavelength. An investigation of the size distribution and crystallinity of CdS_xSe_{1 − x} nanoparticles has been also performed considering those parameters that are mainly influenced by the disorder of the system, such as the extent of the Urbach tail and the Raman bandwidth. Thanks to the results obtained, discrimination between the more recent glass and the older Art Nouveau ones has been verified, leading to the identification of a useful analytical protocol for conservation purposes. Copyright © 2015 John Wiley & Sons, Ltd.     

Paraloid文物保护材料光老化的红外光谱研究

Paraloid(乳胶粘合剂)是一系列丙烯酸树脂的商品名称,是文物保护领域中最常用的保护材料之一,主要用于文物的加固、封护和粘接,适用文物材质范围非常广泛。其中以Paraloid B-72最具代表性,在国内外的文物保护中被大量使用,相关的应用案例、性能评价及其老化机理研究都有较多报道,而Paraloid系列的其他产品却鲜有关注,在国内应用较少,老化性能研究尚未开展工作。该研究系统评价了Paraloid B-72, Paraloid B-44, Paraloid B-48N和Paraloid B-67的光老化性能,采用红外光谱跟踪紫外辐照3 864 h过程中Paraloid材料分子结构变化,对光老化机理进行了深入解析和半定量评测。结果显示,4种Paraloid系列丙烯酸树脂材料中,B-72老化前后颜色和光泽度均没有发生明显变化,B-48N和B-67老化前后色差较大,B-44光泽度降低最多。丙烯酸树脂老化过程中高分子材料内部发生断链反应以及一定程度的交联反应,表现在主要官能团吸收的减弱和羰基指数(CI)的增加。根据主要官能团吸收峰CO相对强度的半定量分析结果反映出,B-72的光稳定性最好,...     

Art galleries with guards of uniform range of vision

We are given an art gallery represented by a simple polygon with n sides and an angle (0°,360°]. How many guards of range of vision are required to monitor every point of the polygon in the worst case? After recent results on upper bounds of this problem, we prove new lower bounds for all 0°<<180°. Several lower bounds meet the best known upper bounds, and we expect our lower bounds to be best possible.

Surprisingly, it turns out that n/3 180°-guards are always enough to monitor a polygon of n sides, but if we wish to use (180−)°-guards for any >0, then possibly 2n/3−1 guards are necessary.     

Art gallery problem with guards whose range of vision is 180

It is shown that in any polygonal art gallery of n sides it is possible to place n/3 point guards whose range of vision is 180° so that every interior point of the gallery can be seen by at least one of them. The guards can be stationed at any point of the art gallery. This settles an open problem posed by J. Urrutia.     

The advent of chemical symbolism in the art of Sonya Rapoport

This paper explores the use of chemical symbolism in works by the new media artist Sonya Rapoport, with a focus on the pivotal Cobalt series from the late 1970s. These works, drawings on computer printouts generated by research at the Lawrence Berkeley Laboratory, respond to experiments in nuclear chemistry. They mark the beginning of three productive decades in which Rapoport produced a variety of images related to chemistry in her work. She states, “I looked for authentic research projects that were interesting to me, preferably with captivating pictorial subject matter. Then came the creative chaotic process of resolving a cohesive product that combined scientific research with art concept.” Rapoport had an unusual degree of access to scientific materials through her husband, organic chemist Henry Rapoport, a faculty member at the University of California, Berkeley. At the time of production, these works were outside mainstream art world interests and they have received little critical attention. This paper examines the development of Rapoport’s images and places her use of chemical references in context in her lifetime of work.