# Characterization of Waves in the Roman Wall Paintings of the Herculaneum Site (Italy)
## 3 Results and Discussion
### Analyses of Archeological Samples
#### 3.2.2. GC/MS  
The wall painting samples AC 17, AC 20 and AC 25 were analyzed to detect, in a single gas chromatographic run, the hydrocarbons, fatty acids and alcohols, the markers chosen for the identification of waxes. In Figure 7 are reported the chromatograms obtained by an analysis of archaeologic samples. Figure 6: Raman spectra from wall painting samples AC 18, AC 21, AC 22, AC 23 and AC 26. The letters indicate the features typical of: **a** aragonite, **c** calcite, **b** Egyptian blue, **q** quartz, **g** gypsum, **h** hematite, **w** wax. Figure 7: Total ion chromatogram of the wall painting samples AC 17, AC 20 and AC 25. For peak identification, see Table 2.  
The presence in the chromatograms of the archaeological samples of long-chain hydrocarbons, long-chain fatty acids and alcohols suggests the presence of waves. From the comparison with the GC pattern of the reference waves (Figure 3a,b), it is evident that more than one type of wax is present in the samples. The bees wax markers, odd long-chain hydrocarbons (C19-C33), with C27 the most abundant; fatty acids, among which palmitic and lignoercic acid are predominant; and C24-C30 alcohols, with prevalent triacontanol, are identified in all of the paint samples [74]. However, in the samples, there is a change in the distribution of the beeswax constituents. In all the wall paint samples, it is possible to note an increase in the content of even hydrocarbons, generally very low in natural waves; a decrease in the characteristic odd \(n\)-alkanes, mainly pentacosane and heptacosane; and greater quantities of triacontane and dotriacontane. It cannot be disproven that the modifications of the hydrocarbon component of beeswax are due to degradation phenomena suffered over time. As reported by several authors, significant differences in the chromatographic profile of ancient beeswax compared to that of contemporary beeswax are often present: in ancient beeswax, the partial modification of the \(n\)-alkane pattern can be due to drastic heating but also to bacterial degradation [45; 47; 48; 75]. The presence of oxalates derived by the oxidation of the lipidic fraction in organic binders, detected both by Raman and FTIR investigation, can support this hypothesis [72; 73]. Triacontane (not found in beeswax) and hentriacontane, numbered 33 and 38 in Table 2, respectively, detected in large quantities in all samples, are candellilla wax identifiers. In addition, the high content of even hydrocarbons is indicative of mineral or artificial waves. In particular, dotriacontane, found in very high quantities in the samples, is abundant in microcrystalline wax (derived from paraffin). In adulterated beeswax, in addition, the content of even hydrocarbons is considerably higher [76; 77]. To better highlight these results, in Figure 8a,b are reported the weight percentage, obtained by the GC data, of the marker compounds (hydrocarbons, fatty acids, alcohols) in contemporary reference waxes and in archaeological samples, respectively. Furthermore, Table 3 shows, as an attempt to differentiate the type of waxes, the ratio between total fatty acid and alcohols and also between total odd and even \(n\)-alkanes. As discussed above, in the contemporary natural waxes investigated, i.e., beeswax, candellilla and carnauba, the content of even hydrocarbons is very low. In mineral or artificial waves, as clearly shown by the histograms, the even hydrocarbons constitute about 45-50% (wt %). Therefore, the odd/even alkane ratio cannot be used to distinguish the type of animal or vegetable waxes, while it allows to obtain some information on the presence of mineral or artificial waxes. Actually, in all three wall painting samples, there was a high content of even \(n\)-alkanes: the OA/EA ratio was about 0.6, compatible with the presence of formulated candellilla (a mix of glyceryl stearate, paraffin, carnauba and candellilla).