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Cage cup

Luxury Late Roman glass vessel type

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Through Microscope

Even rarer are examples with scenes with figures, of which the Lycurgus Cup in the British Museum is the only complete example to survive, though there are other fragments. In this the rest of the "cage" is made up of a vine that entraps Lycurgus. None have a foot. All were clearly difficult to make, and no doubt very expensive, like the other spectacular type of luxury Roman glass, cameo glass objects such as the Portland Vase. Both the technology used to make them and the way they were used are still the subject of some debate among specialists.

Technology

Cage cups, diatreta, are mentioned in Roman literature, and the dates assigned to examples (not necessarily by the same people) range from around the mid-third to the mid-4th century, at the same time as the late Roman cameo glass vessels. They appear to have been made of similar glasses, and there is also evidence that some late vessels may have been combinations of cameo and cage-cup techniques. The main division is between cups with figures, whether or not accompanied by reticulated patterns, and those without. Some have inscriptions and flanges with ovolo decoration; others do not. Most have a narrow beaker shape, but others a wider bowl-like one.

Since the first publication on the subject in 1680 it has mostly been accepted that the cage cups were made by cutting and grinding a blank vessel of solid thick glass, a laborious technique at which the Greeks and Romans were very experienced from their passion for hardstone carvings and engraved gems in semi-precious stones. An alternative theory, once rejected but recently revived, suggests that this is only true of the rim of the vessels and the cutting of the fixed cage, but not for the joining of beaker and its cage; these would have been made separately and fused when hot. For example, it is claimed that the smooth joins on the Munich cup show the fusion of the cage to the main cup, though the cage itself is carved. These smooth joins also show the Cologne and Pljevlja cups above. This remains controversial, and a fragmentary cup found in Corinth in the 1960s is said to show no evidence of joints where the cage meets the main cup when examined under a microscope. Also, the German experimental archaeologist and glass engraver Josef Wenzel has reproduced several historical cage cups, including the Cologne cup, by first shaping a massive cup, adding the coloured glass on the outside as thick bands and plates, then carving them out, as this technology was widespread in the Rhine area, where it was used for gemstone cutting.

Apart from carved gems, a small fragment of an openwork pattern in reticulated silver has survived in a large hoard of Roman silver chopped up in the 5th century as bullion, and buried in Scotland at Traprain Law, now in the Royal Museum of Scotland. The fragment shows a pattern based on circles, that is very similar to the glass diatreta, suggesting that the same style may have been used in silver plate, though which came first is unknown.

Some examples add difficulty to the manufacturing process by using different colours on the cage, like the Milan and Cologne cups, but most are plain glass, like those at Munich and Corning. For the special technology of dichroic glass, which changes colour when light passes through it, see the article on the best example, the Lycurgus Cup.

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