## 1 Introduction  
Scientific research has been interested in the area of archaeology and history for several years, particularly those related to the chemical-physical characterization of materials [1, 2]. Knowledge of the compositional features of the raw materials employed in the making of artworks is an additional tool for understanding the artworks themselves, i.e., their provenance, dating, trade, and manufacturing technology, in addition to their own historical-artistic significance and social framework to which the artwork belongs [3].  
In the case of natural minerals and earths with coloring effects, namely iron and manganese oxides and hydroxides, a complete overview has already been provided [4, 5, 6, 7, 8]. In particular, the presence of pigment pieces of various sizes, pigment powders, and residues, and even paint drops in deposits, like seashells, stone and brick utensils, millstones, vessels of different kinds, and so forth, is well documented [9, 10, 11]. Moreover, the evidence of ochre processing laboratories (comprising raw materials, working tools, and/or holding vessels) in various time periods and locations reveals that the utilization of dyeing raw products was not random but a well-planned activity since prehistory, requiring a significant investment in time and effort in order to procure and process them [12, 13, 14].  
However, a particularly new issue to be considered in this context relates to the characterization of pigments for painting as far as their natural radioactivity content is concerned and, from that, the evaluation of any potential radiation hazard to the health of the public.  
As a matter of fact, natural pigments for painting can be considered environmental matrices due to the presence, in their mineralogical composition, of trace phases containing natural radioisotopes, including decay chains products of primordial uranium (\({}^{238}\)U and \({}^{235}\)U), thorium (\({}^{232}\)Th), and \({}^{40}\)K radionuclide [2; 15; 16]. The attention placed on the aforementioned natural radioisotopes from a health point of view is due to the circumstance that their annual effective dose rate outdoor constitutes more than half of the radiation exposure for the population [2]. As extensively reported in the literature [17; 18; 19; 20; 21], this is a critical point since chronic exposure to uranium and thorium can have various adverse health impacts, such as acute lung disease and leukopenia, head, nose, lung, pancreatic, liver, bone, kidney, and leukemia cancers [22; 23; 24].  
In this regard, the evaluation of the specific activity of the aforementioned natural radioisotopes in pigments for painting can be meaningful for the estimation of background radiation levels in order to assess the effects of radiation exposure on the public [21; 25; 26]. Noteworthy, it represents one of the aims of this study, together with the employment of multivariate statistical analyses to identify possible correlations between the radioactivity content and radiological indices and with the analyzed samples [27; 28]. In particular, investigated pigments were grouped into five clusters, at the highest level of detail, based on chemical nature.