Microchemistry and Microscopy Art Diagnostic Laboratory (M2ADL), University of Bologna-Ravenna Campus, via Guaccimanni 42, 48100 Ravenna, Italy.
Acc Chem Res. 2010 Jun 15;43(6):792-801. doi: 10.1021/ar900274f.
Fourier transform infrared (FTIR) spectroscopy is one of the most widely applied techniques for the investigation of cultural heritage materials. FTIR microscopy is well established as an essential tool in the microdestructive analysis of small samples, and the recent introduction of mapping and imaging equipment allows the collection of a large number of FTIR spectra on a surface, providing a distribution map of identified compounds. In this Account, we report recent advances in FTIR spectroscopy and microscopy in our research group. Our laboratory develops, tests, and refines new and less-studied IR spectroscopy and microscopy methods, with the goal of their adoption as routine analytical techniques in conservation laboratories. We discuss (i) the analysis of inorganic materials inactive in the mid-IR region by means of far-IR spectroscopy, (ii) the development of new methods for preparing cross sections, (iii) the characterization and spatial location of thin layers and small particles, and (iv) the evaluation of protective treatments. FTIR spectroscopy and microscopy have been mostly used in the mid-IR region of 4000-600 cm(-1). Some inorganic pigments, however, are inactive in this region, so other spectroscopic techniques have been applied, such as Raman spectroscopy. We suggest an alternative: harnessing the far-IR (600-50 cm(-1)). Our initial results show that far-IR spectroscopy is exceptionally useful with mural paintings or with corrosion products from which larger sample quantities can generally be collected. Moreover, the inorganic composition of a sample can be characterized by the presence of several compounds that are inactive in the mid-IR range (such as sulfides, oxides, and so forth). Stratigraphical analyses by FTIR microscopy can be hindered by the process of cross section preparation, which often involves an embedding organic polymer penetrating the sample's porous structure. Here, the polymer bands may completely cover the bands of organic compounds in the sample. However, a correct methodological approach can prevent such limitations. For example, it is always advisable to analyze the sample surface before preparing the cross section in order to characterize the preparation layers and the varnish layers, which are generally applied to the surface of a painting both to protect it and improve the color saturation. Furthermore, the innovative use of IR-transparent salts as embedding material for cross sections can prevent contamination of the embedding resin and improve detection of organic substances. Another key point in the use of FTIR microscopy in artwork analysis is spatial resolution. The high-energy output of a new integrated FTIR microscope enhances the ability to characterize and spatially locate small particles and thin layers. Moreover, the new configuration proves extremely useful in the evaluation of protective treatments, because larger areas may be analyzed in less time in comparison to traditional systems, allowing the collection of more statistical data.
傅里叶变换红外（FTIR）光谱是研究文化遗产材料最广泛应用的技术之一。FTIR 显微镜作为对小样本进行微破坏性分析的基本工具已得到充分确立，而最近引入的映射和成像设备允许在表面上收集大量的 FTIR 光谱，从而提供已识别化合物的分布图。在本报告中，我们报告了我们研究小组在 FTIR 光谱和显微镜方面的最新进展。我们的实验室开发、测试和改进新的和研究较少的 IR 光谱和显微镜方法，目标是将其作为保护实验室中的常规分析技术采用。我们讨论了（i）通过远红外光谱分析在中红外区域不活跃的无机材料，（ii）用于制备横截面的新方法的开发，（iii）薄涂层和小颗粒的特征和空间定位，以及（iv）保护处理的评估。FTIR 光谱和显微镜主要用于 4000-600cm(-1) 的中红外区域。然而，一些无机颜料在该区域不活跃，因此应用了其他光谱技术，例如拉曼光谱。我们建议使用另一种方法：利用远红外（600-50cm(-1)）。我们的初步结果表明，远红外光谱对于壁画或可以从其收集一般来说更大样本量的腐蚀产物非常有用。此外，通过存在在中红外范围内不活跃的几种化合物，可以表征样品的无机组成（例如硫化物、氧化物等）。通过 FTIR 显微镜进行的层状分析可能会受到横截面制备过程的阻碍，该过程通常涉及穿透样品多孔结构的嵌入有机聚合物。在这里，聚合物带可能完全覆盖样品中有机化合物的带。但是，正确的方法方法可以防止这种限制。例如，在制备横截面之前，始终建议分析样品表面，以便对制备层和清漆层进行特征分析，这些层通常都涂在绘画的表面上，以保护它并提高颜色饱和度。此外，将 IR 透明盐用作横截面的嵌入材料的创新用途可以防止嵌入树脂的污染并改善对有机物质的检测。在艺术品分析中使用 FTIR 显微镜的另一个关键点是空间分辨率。新集成的 FTIR 显微镜的高能量输出增强了对小颗粒和薄层进行特征和空间定位的能力。此外，新配置在保护处理的评估中非常有用，因为与传统系统相比，它可以在更短的时间内分析更大的区域，从而收集更多的统计数据。
