Institute for Conservation and Valorization of Cultural Heritage (ICVBC) - National Research Council, Via Madonna del Piano 10, 50019 Sesto Fiorentino - Florence, Italy.
Analyst. 2019 Mar 25;144(7):2375-2386. doi: 10.1039/c8an02426j.
Red stains are a common discolouration on stone cultural heritage all over the world. These are very difficult to remove and little is known about the reddish pigmentation. Numerous red stains were mapped on the Baptistery of San Giovanni in Florence, one of the most important monuments in Italy. This paper is focused on red stains on marble stone and the results of a detailed multidisciplinary approach are presented. Several analytical and investigation techniques (such as optical microscopy, X-ray fluorescence mapping, X-ray micro-tomography, micro-Raman spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, microbial isolation, colorimetric measurements and isotopic analyses) were used to better understand the origin and processes involved in this kind of alteration. Analyses of the red stains led us to believe the presence of minium (lead tetroxide) and Pb are usually concentrated in the spaces between calcite grains. Red stains of Pb isotopic composition also overlap with data from Sardinian mines. These preliminary data seem to reinforce the suggestion of a source of lead from some metallic items (during restoration campaigns between 1938 and 1944, damaged parts were removed and replaced, and the new marble cladding was fixed with iron brackets treated with minium).
红色污渍是世界各地石质文化遗产的一种常见变色现象。这些污渍非常难以去除，而且对于红色颜料的了解甚少。在佛罗伦萨的圣乔瓦尼洗礼堂（意大利最重要的纪念碑之一）上绘制了许多红色污渍。本文主要关注大理石上的红色污渍，并介绍了详细的多学科研究方法的结果。使用了多种分析和研究技术（如光学显微镜、X 射线荧光映射、X 射线微断层扫描、微拉曼光谱、带有能量色散光谱的扫描电子显微镜、微生物分离、比色测量和同位素分析），以更好地了解这种变质过程的起源和涉及的过程。对红色污渍的分析使我们相信存在密陀僧（四氧化铅）和 Pb，它们通常集中在方解石晶粒之间的空隙中。Pb 同位素组成的红色污渍也与来自撒丁岛矿山的数据重叠。这些初步数据似乎进一步证实了来自某些金属物品（在 1938 年至 1944 年之间的修复活动期间，移走了受损的部分并进行了更换，新的大理石覆层用经过密陀僧处理的铁支架固定）的 Pb 来源的说法。
