Chapoulie Rémy, Cazenave Sandrine, Duttine Mathieu
CRP2A (Laboratory of Physics for Archaeology), CNRS UMR 5060 IRAMAT, Université Michel de Montaigne Bordeaux 3, Maison de l'Archéologie, 33607 Pessac, France.
Environ Sci Pollut Res Int. 2008 May;15(3):237-43. doi: 10.1065/espr2007.07.436.
Most historical buildings in Bordeaux city are made of limestone. This yellowish-white rock is rather porous and highly sensitive to pollution. As a consequence of local weathering conditions, these buildings present a dark appearance due to the development of a superficial dark grey to black crust.
For the last decade, a campaign has been underway to clean these buildings. Eleven techniques of surface treatment have been used, including laser beam technology. As a contribution to the study of laser beam effects on stone buildings, two analytical methods have been used on clean versus unclean surfaces: Cathodoluminescence (CL) and Electron Paramagnetic Resonance (EPR), in addition to SEM-EDX and XRD.
The black crust is composed of different types of particles: carbon porous micro-particles of industrial origin, atmospheric dust due to the erosion of soils and rocks, alumino-silicate particles from urban pollution; all these particles being cemented by gypsum.
As far as heritage conservation is concerned, the laser surface treatment not only preserves the original patina of the stone, but also leaves surface smoothness unaltered.
CL and EPR data confirm that lasers--with highly controlled parameters--only get rid of the black crust and, thus, reveal the underneath layer, the so-called patina. This patina shows no luminescence, whereas the limestone on which it has grown shows a bright orange emission of CL. This indicates CL to be a fast and easy way to provide a high quality control for the restoration of polluted ancient stones.
波尔多市的大多数历史建筑由石灰石制成。这种黄白色岩石孔隙较多，对污染高度敏感。由于当地的风化条件，这些建筑因表面形成深灰色至黑色的硬壳而呈现出暗沉的外观。
在过去十年中，一直在开展清洁这些建筑的行动。已经使用了11种表面处理技术，包括激光束技术。作为对激光束对石材建筑影响研究的贡献，除了扫描电子显微镜-能谱仪（SEM-EDX）和X射线衍射仪（XRD）外，还在清洁和未清洁的表面上使用了两种分析方法：阴极发光（CL）和电子顺磁共振（EPR）。
黑色硬壳由不同类型的颗粒组成：工业来源的碳多孔微粒、土壤和岩石侵蚀产生的大气尘埃、城市污染产生的铝硅酸盐颗粒；所有这些颗粒都由石膏胶结在一起。
就遗产保护而言，激光表面处理不仅保留了石材的原始光泽，而且还保持了表面光滑度不变。
CL和EPR数据证实，在参数得到高度控制的情况下，激光仅能去除黑色硬壳，从而露出其下的所谓光泽层。该光泽层不显示发光，而其生长其上的石灰石显示出明亮的橙色CL发射。这表明CL是一种快速且简便的方法，可为受污染古代石材的修复提供高质量控制。
