Genuine ultramarine has been one of the most precious blue pigments employed since ancient times. It used to be obtained by crushing and grinding the lapis lazuli rock and selectively extracting the blue mineral lazurite. Since 1828, when it was produced the synthetic version, the use of this much less expensive material became widespread and synthetic ultramarine blue replaced the natural one in painting palettes. The distinction between natural and synthetic ultramarine is, therefore, an important goal in authentication issues. Here, we present a hyperspectral microRaman imaging analysis, complemented with the characterization of ultramarine pigment samples in terms of colour, elemental composition and identification of crystalline phases by means of fiber optics reflection spectroscopy (FORS), X-Ray Fluorescence (XRF) and X-Ray diffraction (XRD), respectively. We show that a characteristic luminescence signature, easily detected in the course of standard Raman spectroscopic analysis using 785 nm as excitation, is indicative of the natural origin of the ultramarine blue pigments. Furthermore, simultaneous Raman/luminescence hyperspectral microimages allow the distinction between natural pigments of different quality thanks to the different intensity and spatial distribution of the lazurite characteristic band at 548 cm⁻¹ and those of the luminescent impurities in the region between 1200 and 2000 cm⁻¹. The establishment of a range of quality between different samples of lapis lazuli was also attempted taking into account the variations in the intensity of the Raman bands located at 548 cm⁻¹ and 1286 cm⁻¹. Finally, the feasibility of using the simultaneous Raman/luminescence features for authentication of ultramarine blue in a real historical context, even with non-invasive investigations, is illustrated with examples of different types of blue decorations from several halls of the Alhambra monumental ensemble, in Granada.

真正的群青一直是自古以来使用的最珍贵的蓝色颜料之一。过去，它是通过将青金石岩石粉碎和磨碎并选择性地提取蓝色矿物天青石而获得的。自1828年开始生产合成版本以来，这种便宜得多的材料就得到了广泛使用，人造深蓝色代替了绘画调色板中的天然深蓝色。因此，天然和合成群青的区别是认证问题的重要目标。在这里，我们介绍了高光谱显微拉曼成像分析，并通过颜色反射，颜色成分，通过光纤反射光谱法（FORS）鉴定结晶相来表征群青色素样本，X射线荧光（XRF）和X射线衍射（XRD）。我们表明，在使用785 nm作为激发的标准拉曼光谱分析过程中易于检测到的特征性发光特征，表明群青蓝色颜料的天然来源。此外，由于拉曼石特征谱带在548 cm处的强度和空间分布不同，因此同步拉曼/发光高光谱显微图像可以区分不同质量的天然颜料^-1和在1200至2000 cm ^-1之间的区域中的发光杂质。考虑到位于548 cm ^-1和1286 cm ^-1的拉曼谱带强度的变化，还尝试在青金石的不同样品之间建立质量范围。最后，以阿罕布拉纪念性合奏的几个大厅中不同类型的蓝色装饰为例，说明了即使在进行非侵入式调查的情况下，在真实的历史背景下使用拉曼/发光体同时特征鉴定群青的可行性。格拉纳达