Majolica oxides

The white glazing of some of the modem majolica is composed of felspar, borax, and the oxide of tin. This glazing, ns well as the colors, is frequently applied directly to the biscuit ware, which considerably reduces tho labor of ornamentation, without detracting from the beauty of the manufacture. 

Majolica is an earthenware pottery characterized by a creamy light-buff-colored paste and an opaque white tin-lead glaze coating the entire outer surface of the vessel. However, the most outstanding feature of the majolica pottery perhaps lies in its decoration, being the subject of numerous studies by art historians. Majolica decorations are produced from metallic oxides that always are applied on top of the tin glaze. 

Table I. Concentration of Oxides in Majolica from Spanish...

Figure 8. Computer projection of three-dimensional plot of cerium, lanthanum, and thorium oxide concentrations for Spanish Colonial majolica sherds. The data divides into a group having its source in Spain and a group whose source is Mexican, as discussed in the text.

In Figure 8 we have plotted the lanthanum oxide, cerium oxide, and thorium oxide concentrations for sherds excavated in the Dominican Republic and Venezuela and sherds from the Metro excavations using a computer system developed for this purpose at Brookhaven National Laboratory (8). On the basis of these three oxides there is a distinct separation between the sherds from the Dominican Republic and Venezuela and those from Mexico City. Unlike the sherds from the Dominican Republic and Venezuela, the sherds from Mexico City appear not to have originated in Spain, at least at that specific source. There is further evidence of this distinction between the two sets of sherds. X-ray diffraction analysis of the samples from Jerez and from the New World showed that the sherds from Jerez, the Dominican Republic, and Venezuela had intense quartz peaks whereas the sherds from Mexico City did not. This constitutes additional evidence that the majolica from Mexico City came from a different source than the majolica from the Caribbean sites. 

Table I gives the values used for the USGS standard rocks both at Brook-haven National Laboratory and in the Conservation Analytical Laboratory of the Smithsonian Institution. The values reported for the Smithsonian were obtained by preparing the USGS standard rocks by using the method described earlier and analyzing them using NBS Glass Standards 610 and 612 and Spex Industries Atomic Absorption Standards. Twenty-four samples of majolica that had been analyzed by INAA were analyzed for comparison using DCP-OES. The data for three of these samples are given in Table II. Additional comparative data exist for SA 67, 76, 77, 84, and 94 and SC 03-21 for the 15 oxides that appear in Table II and in Reference I.

The chemical composition of imported, European-made majolica is different from that of majolica made in Mexico (J). The difiFerences in the concentrations of the oxides of cerium, lanthanum, and thorium are eaily recognized the Spanish majolica contains approximately twice as much of each of these oxides as the Mexican majolica. The mineralogical composition, too, of the pottery products of each area is fundamentally different and can easily be identified. The ceramic types and their origins, based on archaeological arguments, can be found in Table I. 

Second, two specimens shown in Table I—one believed to have been made in Europe (SB 33), the other of questionable Mexican origin (SB 32)—contain volcanic temper and, therefore, belong to the New World production. Both specimens contain the cerium, lanthanum, and thorium oxide concentrations characteristic of Mexican majolica. 

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