# Characterization of Waves in the Roman Wall Paintings of the Herculaneum Site (Italy)
## 3 Results and Discussion
### Analyses of the Reference Wax Samples
#### 3.1.2 GC/MS

Table 2: Identified compounds in theIn beeswax (Figure 3a), odd-numbered long-chain hydrocarbon (C21-C33) and unsaturated hydrocarbons (C31:1 and C33:1) were identified. C27 is the most abundant hydrocarbon, followed by C31, C25 and C29 in decreasing order. Hydrocarbons with an even carbon number are also found in low amount. Long-chain even-carbon-number linear fatty acids (from C14 to C34) and linear alcohols (ranging from C24 to C34, myricylic alcohol being the predominant one) were also identified. Palmitic acid was the most abundant in the pure beeswax, followed by the lignoercic acid. Palmitic acid C16, \(n\)-heptacosane (C27) and nonacosane (C29) are diagnostic for beeswax [29; 32; 52; 53]. Palmitic acid and myricylic alcohols originate from the hydrolysis of myricyl palmitate, the representative ester of beeswax. Spermaceti (Figure 3a) wax is characterized by long-chain alcohols (ranging from C12 to C20) and no hydrocarbons being present. The main alcohols are 1-octadecanol (C18, stearyl alcohol) and 1-hexadecanol (C16, named cetyl alcohol or palmityl alcohol). In the chromatograms, with a longer retention time, the peak of cetyl palmitate (the ester of cetyl alcohol and palmitic acid, \(C_{15}H_{31}COO\)-\(C_{16}H_{33}\)), which is the characteristic component of spermaceti, is found [29; 30]. The chromatographic profile of lanolin is very complex (Figure 3b), and the identification of all compounds is difficult. Lanoline is very rich in odd- and even-carbon-number fatty acids (from C10 to C29) linear and branched; their isomers are also found. The landine's alcohol content varies greatly and remains high, with odd and even carbon numbers ranging from C12 to C29 showing the highest values in 1-icosanol (C20 arachtidyl alcohol), 1-heneicosanol (C21) and docosanol (C22 behenyl alcohol) [52]. In candellilla wax, odd- and even-numbered long-chain hydrocarbons from C22 to C33 were found, among which C31 constituted 80%, as reported in the literature [30]. The C30 hydrocarbon was detected only in candellilla. In addition, long-chain fatty acids, from C16 to C32, the most representative being montanic acid (C28), and long-chain alcohols, from C24 to C30, were identified. Carnauba contains saturated fatty acids with even chain length ranging from 16 to 28 carbon atoms, among which behenic acid (C22) and lignoercic acid (C24) were the main components, and long-chain alcohols (C22-C30), triacontanol being the most abundant, in agreement with the results of other authors [29; 53; 54]. Paraffin, formulated candellilla and microcrystalline wax (Figure 4) show very similar chromatogram profiles. They are characterized by high contents of odd- and even-carbon-number \(n\)-alkanes ranging from C22 to C33 and by very small contents of fatty acids. Paraffin and microcrystalline waxes do not contain alcohols. Figure 4: Comparison of the GC traces of the mineral and artificial waxes. The peak number is reported in the first column of Table 2.  
Paraffin is a coal-derived wax. Generally, the paraffin's chromatogram shows a distribution of alkanes centered on the heptacosane (C27), but slight variations in their distribution may occur, depending on the raw petroleum distilled. In microcrystalline wax, the main \(n\)-alkanes are tetracosane (C24) and pentacosane (C25), and the main acid is the docosanoic acid (C22) [55; 56]. The formulated candellilla is a mixture of paraffin, glyceryl stearate (C\({}_{21}\)H\({}_{42}\)O\({}_{4}\)) and a low content of carnauba and candellilla waxes. Its chromatogram is characterized by homologous series of \(n\)-alkanes with odd and even carbon number in the range C19 to C33 (the main one is C24), such as in paraffin, a high content of palmitic and stearic acid and a low content of C16, C18 and C30 alcohols, due to the hydrolysis of glyceryl stearate and wax esters. The compounds identified by the CG-MS analyses are summarized in Table 2.