Albert-Tortosa Francesc, Jiménez Núria, Pradell Trinitat, Butí Salvador, Beltran Victoria, Font Lídia, Salvadó Nati
Departament d'Enginyeria Química, Universitat Politècnica de Catalunya·BarcelonaTech (UPC). EPSEVG, Av. Víctor Balaguer s/n, 08800, Vilanova i la Geltrú, Barcelona, Spain.
Departament de Física, Centre de Recerca en Ciència i Enginyeria Multiescala de Barcelona, Universitat Politècnica de Catalunya·BarcelonaTech (UPC), Campus Diagonal Besòs, Av. Eduard Maristany, 10-14, 08019, Barcelona, Spain.
Sci Rep. 2025 May 27;15(1):18583. doi: 10.1038/s41598-025-03620-5.
The formation of lead apatites in heritage objects is increasingly recognized as a recurrent phenomenon, however their origins and formation mechanisms remain poorly understood. This study explores the process behind the darkening and surface clouding in Roman fresco paintings, providing novel insights into the formation of lead-calcium phosphates, PbCa(PO)Cl(OH), and plattnerite, β-PbO, from the pigment minium, PbO, linked to interactions with environmental factors and dust deposition. A combination of microanalytical techniques was used, including optical microscopy, scanning electron microscopy and elemental analysis, synchrotron-based X-ray diffraction and Raman and FTIR spectroscopy. The results show that slightly acidic rainwater or atmospheric moisture reacts with the minium and the calcium carbonate present in the wall painting's binder, resulting in the formation of plattnerite and the release of Pb and Ca ions, while the environment supplies chloride and phosphate ions, present in the infiltrating water. This process culminates in the precipitation of the lead-calcium apatite, due to its high stability. This apatite acts as a cement that incorporates dust and organic residues, forming a layer several tens of micrometres thick that tends to expand outwards. These findings contribute to a better understanding of pigment degradation mechanisms and will help inform conservation strategies.
文物中铅磷灰石的形成日益被认为是一种反复出现的现象，然而其起源和形成机制仍知之甚少。本研究探讨了罗马壁画变黑和表面起雾背后的过程，为从颜料铅丹（PbO）形成磷酸铅钙（PbCa(PO)Cl(OH)）和四方铅矿（β-PbO）提供了新的见解，这与环境因素和灰尘沉积的相互作用有关。使用了多种微观分析技术，包括光学显微镜、扫描电子显微镜和元素分析、基于同步加速器的X射线衍射以及拉曼光谱和傅里叶变换红外光谱。结果表明，微酸性雨水或大气湿度与壁画粘合剂中存在的铅丹和碳酸钙发生反应，导致四方铅矿的形成以及铅和钙离子的释放，而环境提供了渗透水中存在的氯离子和磷酸根离子。由于其高稳定性，这一过程最终导致铅钙磷灰石沉淀。这种磷灰石起到了一种胶结物的作用，它结合了灰尘和有机残留物，形成了一层几十微米厚的层，并且倾向于向外扩展。这些发现有助于更好地理解颜料降解机制，并将为保护策略提供参考。
