"Laboratory Studies of Some European Artifacts Excavated on San ...

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Brill, R. H., et al. "<strong>Laboratory</strong> <strong>Studies</strong> <strong>of</strong> <strong>Some</strong> <strong>European</strong> <strong>Artifacts</strong> <strong>Excavated</strong> on San Salvador Island." Columbus and his World: Proceedings <strong>of</strong> the First San Salvador Conference. Ft. Lauderdale, FL: The Station, 1987. pp. 247-292. © Gerace Research Centre. Used with permission. www.geraceresearchcentre.org The high lead content <strong>of</strong> the San Salvador beads produced a glass with a low s<strong>of</strong>tening point which would have allowed it to have been drawn out in threads and wound around a wire at relatively low temperatures. From the viscosity-temperature curve for a very similar glass, we estimate that glasses with the composition <strong>of</strong> the San Salvador beads would have been s<strong>of</strong>t enough to have been worked in this manner at a temperature <strong>of</strong>750-800°C. This would be some 250-300° lower than required for a soda-lime glass. It is probable that such beads could have been made with an alcohol lamp equipped with a small blowpipe. One could visualize a kind <strong>of</strong> cottage industry in which cullet, or perhaps glass already drawn into thin rods or threads, was s<strong>of</strong>tened and formed into the beads in small workshops. Indeed, it is difficult to visualize how such tiny beads could have been made at all in large numbers if the glass would have had to have been worked at the glory hole <strong>of</strong> a furnace. Although copper produces a blue transparent color in soda-limes and other common glasses, the sparkling, bright green <strong>of</strong> these beads is typical <strong>of</strong>the color produced by copper in a high-lead matrix. The yellowish amber glass is probably a so-called "carbon amber." 13 The yellow opaque bead (5721) from Colombia is obviously colored with the PbSn0 3 yellow colorant-opacifier. (Microscopic flakes <strong>of</strong> the pigment can be seen in the glass.) This pigment is related to the better-known Pb 2 Sb 2 0 7 antimony compound used in ancient glasses. The tin pigment gradually replaced the antimony pigment starting sometime around the 1st-2nd cent. A.D.14 Although both were used from time-to-time after that, the tin-containing pigment, judging from analyses <strong>of</strong> mosaic tesserae, appears to have seen somewhat wider use from Medieval times onward. IS The analyzed chemical compositions <strong>of</strong> the six glasses were used to back-calculate batch formulas which could have been used to prepare the glasses. The mean <strong>of</strong> the PbO:Si0 2 ratio is 2.94, indicating that the basic recipe, on a weight basis, was probably 3.0 parts <strong>of</strong> litharge to 1.0 part <strong>of</strong> sand. The deviation <strong>of</strong> the calculated ratio from this ideal 3:1 ratio is only about 2 relative percent. This deviation is readily accounted for by the alumina, iron, and other impurity oxides which affect the calculation. Transformed to a volume basis, the basic recipe is very close to a 1:1 ratio <strong>of</strong> sand to litharge 16 with a deviation amounting to only 6%. Both <strong>of</strong> these recipes conform to common sense, and the choice <strong>of</strong> one over the other depends only upon whether one chooses to believe that glassmakers <strong>of</strong> the period worked with weight batches or with volume batches. 17 In either case, a small quantity <strong>of</strong>copper-containing colorant was also added to form the green color. We believe this was in the form <strong>of</strong> an oxide scale from a piece <strong>of</strong>scrap brass. Calculations show that the colorant could have been an alloy with a composition 78Cu: 19Zn: 3Sn. This is reasonable for a brass <strong>of</strong> the period. 18 One further point deserves consideration. The composition <strong>of</strong> these glasses is actually closer to the composition <strong>of</strong> enamels than it is to glasses 252 Rakow Research Library, The Corning Museum <strong>of</strong> Glass - http://www.cmog.org
Brill, R. H., et al. "<strong>Laboratory</strong> <strong>Studies</strong> <strong>of</strong> <strong>Some</strong> <strong>European</strong> <strong>Artifacts</strong> <strong>Excavated</strong> on San Salvador Island." Columbus and his World: Proceedings <strong>of</strong> the First San Salvador Conference. Ft. Lauderdale, FL: The Station, 1987. pp. 247-292. © Gerace Research Centre. Used with permission. www.geraceresearchcentre.org ordinarily used for vessel manufacture. It would not be surprising to find that these beads originated in some location where glass or metal enameling was practiced. In summary, the San Salvador beads are all very closely related to one another, and to the four comparative beads from early Spanish Colonial sites in The New World. They are a distinctive and recognizable type visually, were made by the relatively rare wire-wound technique, and share an unusual chemical composition which can be explained on a reasonable technological basis. The next question arising is where these beads might have been made. The possibilities which come to mind are Spain, Portugal, and Venice. The authors have not yet had opportunities to investigate this question as thoroughly as required, and glass specialists consulted so far have been helpful but have not provided definitive answers. Venice is always first among the usual suspects rounded up as the source <strong>of</strong> any glass bead. Although records exist which document the export <strong>of</strong> Venetian beads through commercial trading centers (including Lisbon) it would do an injustice to Spanish glass industries <strong>of</strong> the time to settle too hastily upon Venice in this instance. There were fluorishing glass industries in Spain at the time <strong>of</strong> Columbus's departure, and they should be considered prime candidates for the place <strong>of</strong>manufacture. Elena Ramirez-Montesinos has told us she believes that green glass beads with very high lead contents might have been made at Maria or Puebla de Don Fadrique. The Metal Buckles The two excavated buckles, ( 4691 and 4692) are illustrated in Figures 3 and 4. No. 4692 is quite small, measuring 2.4 cm across the straight shank. It might have been a shoe buckle. No tongue was found to accompany this buckle but perhaps it never had one. It is said that imitation buckles, never intended to be worn, were sometimes made for use as trade trinkets. Such buckles would not show any wear along the straight side where the tongue would have been mounted. Indeed, this buckle does not show such wear, but one wonders if a real buckle would show wear either if it were this heavily corroded. For the moment then, this point remains unresolved. Jaime Barrachina has recently published the archaeological finds excavated at El Castell de Llinars del Valles, a castle near old Barcelona. 19 Among the finds were assorted types and sizes <strong>of</strong> bronze and/or brass buckles,. some <strong>of</strong> which resemble the San Salvador buckle in form and in size. In a personal communication Dr. Barrachina has stated that the example he sees as being the closest parallel for the San Salvador find 20 was common in the early 15th century at his site, and that that type was made until at least as late as 1485. There are two differences between the buckles from Llinars and the San Salvador object. The groove for the tongue in the San Salvador buckle is triangular in section, as ifit (or the prototype for the mold in which it was 253 Rakow Research Library, The Corning Museum <strong>of</strong> Glass - http://www.cmog.org
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