## 4 Discussion  
The structure of the wall painting fragments discovered in the Roman baths from Alburmus Maior showed a typical three-layer structure: a mortar layer (_arricio_), a fine plaster layer (_intonaco_), and a paint layer [24]. Combined analysis highlighted a very common Roman color palette mainly based on mineral pigments--red ochre (hematite), yellow ochre (a mix of hematite and most probably goethite as well), manganese-rich ochre (possible braunite), and carbon black. All identified pigments fall in the category of _colors austeri_ (plain colors) as defined by [PERSON] [9; 49]. Compared to the color palette identified on second century wall paintings from _[PERSON]_[6], or within the painting hall with hypocauats from [PERSON] [11], the palette from Alburmus Maior is plainer. No costly pigments (_colors floridi_) such as minium, cinnabar, azurite, or malachite were found. The use of mainly naturally occurring earth pigments within the baths' decoration from Alburmus Maior suggests that the bathing facility was not intended for the elite (Roman officials) [49]; the historical and archaeological data indicate that the bathhouse operated in an area frequented by administrative staff, soldiers, and civilians [5]. Given the large areas of lost polychromy, an exact assessment of the full range of colors initially employed for the decorations within the Roman baths from Alburmus Maior is not possible. If costly pigments typically restricted to particularly luxurious decorations can be excluded in this case, a wider range of _austeri_ pigments (e.g., green earths, umbers) or pigment mixtures could have been used. In terms of painting technique, the presence of a protein binder could be clearly identified in some of the samples by FTIR analysis. An organic binder such as egg, glue, or animal fat may have been used [24]. These findings, along with the absence of any technical hallmarks of _a fresco_ painting, are clear indicators that at least some of the pigments were applied with the _seco_ technique [16]. The high concentration of calcium carbonate registered within the pigmented areas most probably indicates that a lime rendering (whitewash) was applied, common for both _a fresco_ and _a secco_[47]. Previous studies performed on wall painting fragments discovered at Ulpia Traiana Sarmizegetusa [6] indicated the use of a _fresco-secco_ technique, with lime used as a binder. None of the FTIR spectra registered in those studies showed any signal for organic compounds potentially used as binders. However, the accurate identification of binders could have been affected by various factors: degradation of the original compounds, limited number of samples, or small sampling areas [47]. These same limitations could also explain why a protein signal was observed only in some of the investigated samples from Alburmus Maior. The hypothesis of using a different painting technique at a Roman nearby site from the same period is unlikely. Based on the findings from Alburmus Maior, new wall painting fragments from Ulpia Traiana Sarmizegetusa were investigated in terms of painting technique. Figure 10 presents the imaging documentation of one of the new samples investigated: a wall painting fragment showing red and yellow ochre decorations. UV fluorescence examination highlighted a strong fluorescence of the yellow ochre pigmented areas on the left half of the sample, which, in the visible spectrum, are almost indistinguishable. Based on the fact that iron oxides/ochres lack fluorescence as they absorb UV light, the registered fluorescence is most probably due to the presence of an organic binder [53]. The hypothesis that the fragment comes from an _a secco_ painting is also sustained by the texture of the surface. As it can easily be observed in raking light, the surface is rough, meaning that the plaster contained a great proportion of sand, but also that the surface was not polished--an operation which was used not for esthetical reasons, but for technical reasons.