A Fragment of a Dichroic Cage Cup in The British Museum
All About Glass
Among the glass in the Department of Greek and Roman Antiquities at The British Museum is a fragment of a late Roman dichroic cage cup. Although the fragment has been mentioned on several occasions,1 it has never been described in detail. The find-place is unknown.
The fragment (Fig. 1) consists of parts of the rim and upper wall of a bell-shaped cage cup. The height of the fragment is 6.3 centimeters (cm). The diameter of the rim is 14 cm. The thickness of the fragment, including the openwork, is 0.9 cm, and the thickness of the wall itself is 0.2 cm.
In reflected light, the glass is dull and opaque grayish green; olive green is an appropriate description (Fig. 2). In transmitted light, however, the glass is transparent, and it varies in color from reddish orange (where it is thickest) to lighter, somewhat yellowish orange (where it is thinner) (Fig. 3). The difference between the colors is less dramatic than on the Lycurgus Cup,2 but there is no doubt that the glass is dichroic.
The rim is outsplayed. It has a rounded lip and a small horizontal rib near the junction with the wall.
The upper wall is straight, and it tapers slightly. Near the top of the wall is an openwork Latin inscription with letters 1.8 cm high. Two complete letters and parts of three other letters survive: “]IVAS I[ .” The first I and the S are complete. The surviving parts of the other letters are consistent with reading them V, A, and I, although in the case of the last letter M and F are also possible.3 The meaning of the fragmentary inscription is discussed below.
Of the cage, only a very short part of the border, parts of two adjoining meshes, and the stumps of eight bridges survive. This is sufficient, however, to determine that the upper part of the cage resembled that of other bell-shaped cage cups. A horizontal border supported on a row of bridges enclosed the uppermost row of adjoining meshes, which were roughly circular, but with the height somewhat greater than the width. Each mesh was supported on bridges at the junction with the border, at the junctions with the adjoining meshes, and presumably at the junction with the corresponding mesh in the row beneath it. Where the meshes touch the border, the bridges are concealed by small elements shaped like half a cross. Where the bridges support the junctions of meshes, they are concealed by cruciform motifs.
The Manufacturing Process
A thick-walled blank was made by glassblowing. After annealing, cold working processes were used to remove part of the glass in order to create the inscription and cage.
Technically, the fragment is strikingly similar to the Lycurgus Cup.4 We have inspected both objects closely. The interior surface of neither was cold worked. There are no grinding or polishing marks, and bubbles near the surface of the glass can be seen and felt as slight blisters. Furthermore, there are no cross-sectioned bubbles, such as would occur if the surface had been cold worked. The fire-polished interior surfaces of both this fragment and the Lycurgus Cup are consistent with forming them by glassblowing.
Additional evidence for glassblowing (which is easy to observe in the Lycurgus Cup but less obvious in the fragment) is the vertically aligned elongation of the bubbles trapped in the glass. This effect is most pronounced at the fragment’s midpoint, and it indicates that a thick-walled sphere was elongated on the blowpipe to achieve the object’s final form.5
By contrast, if the blanks for this and other cage cups had been made by a casting process, as has been argued,6 the bubbles closest to the interior surface could not have caused the blisters noted above, since contact with the mold would have prevented any distortion of the wall. Moreover, casting is a static process that invariably leaves the bubbles spherical, a phenomenon we have not observed in ancient cage cups.
In principle, the techniques of cold working used in antiquity—mostly grinding with rotating wheels—are well understood.7 The tools and techniques employed to create cage cups have been the subjects of separate investigations by Josef Welzel8 and the late George D. Scott.9 These authorities agree that the extensive undercutting was carried out with thin, small-diameter rotating wheels attached to a long, narrow shaft, and that the polishing of the bridges and the cage was achieved by handworking with files and other small tools.
The Dichroic Glass
Chemical analyses of late Roman dichroic glasses reveal that the effect was created by the addition to the batch of minute amounts of gold and silver (in the Lycurgus Cup, the quantities are 40 parts per million (ppm) gold and 300 ppm silver, and in the fragment that forms the subject of this note the quantities are 13 ppm gold and 2,270 ppm silver). However, the simple presence of gold and silver does not produce dichroism, which depends on the formation of nanoparticles of gold-silver alloy by a process of heat treatment.10 This process was highly unusual, and the difficulty of controlling it presumably accounts for the differences in the colors of Roman dichroic glass. The number of published late Roman examples is very small (about a dozen), and it is interesting to note that roughly half of these objects are cage cups or related vessels with openwork decoration. The following is a list of openwork vessels made of dichroic glass:
1. The Lycurgus Cup.11
2. The “Dionysiac” fragment in The Metropolitan Museum of Art, which was acquired in Rome.12
3. The bucket in the Museo Arqueologico Nacional, Madrid, which was found at Soria (ancient Termes), Spain.13
4. A fragment in the Antiquarium of the Roman Forum, which was found in Rome.14
5. A fragment in The Corning Museum of Glass.[^^78.1.17^^]15
6. A fragment found during excavations at Duluk Baba Tepesi (ancient Doliche), Turkey.16
7. The fragment described in this note.
If we accept the reading of the first four letters as ]IVAS, they are readily explained as part of the word VIVAS (“may you live”), a component of the toast “BIBE VIVAS MVLTIS ANNIS” (drink; may you live for many years), which is found on the Trivulzio Cage Cup.17 The detached fifth letter is more difficult to interpret because only the bottom and the lower attachment survive. Harden and Toynbee believed it might be M. This requires the two vertical strokes to converge at the bottom, and this is the case with the M on the Trivulzio Cage Cup.18
If the letter had a single vertical stroke, the most likely options appear to be F and I. If the letter was F, the surviving part of the inscription may have been “VIVAS F[ELICITER” (may you live happily [or fortunately]) or something similar, as is apparently the case on a fragmentary cage cup from Fejer County, Hungary.19
If, on the other hand, the letter was I, the inscription may have included the words “VIVAS IN DEO” (live in God). This is how L. Nagy expanded the letters “VASM” or “VASI” on a fragmentary cage cup (now lost) from Oszony (ancient Brigetio), Hungary.20 Similar inscriptions can be seen on late Roman scratch-engraved objects— a bowl found in Cologne has an inscription that includes the words “GAVDIAS IN DEO” (rejoice in God)21— but no such inscription has been reported on a cage cup.
Only a handful of late Roman vessels are known to have been made of dichroic glass. Approximately half of these objects are cage cups or related vessels. Presumably the combination of dichroic glass and openwork decoration was considered remarkable by late Roman users of luxurious glassware.
William Gudenrath with David Whitehouse
This article was published in the Journal of Glass Studies, Vol. 51 (2009), 224–227.
1 1953.10-22.2: D. B. Harden and Jocelyn M. C. Toynbee, “The Rothschild Lycurgus Cup,” Archaeologia, v. 97, 1959, pp. 179–212, esp. pp. 209–210, no. B7; Robert H. Brill, Chemical Analyses of Early Glasses, Corning: The Corning Museum of Glass, 1999, v. 1, p. 79, and v. 2, p. 146, no. 389; Ian Freestone and others, “The Lycurgus Cup—A Roman Nanotechnology,” Gold Bulletin, v. 40, no. 4, 2007, pp. 270–277, esp. p. 275 and fig. 3.
2 Harden and Toynbee [note 1]; Donald B. Harden and others, Glass of the Caesars, Milan: Olivetti, 1987, pp. 245–249, no. 139.
3 We are grateful to Dr. Paul Roberts, assistant keeper at The British Museum, for his comments on the inscription.
4 Veronica Tatton-Brown, “The Roman Empire,” in Five Thousand Years of Glass, ed. Hugh Tait, London: British Museum Press, 1991, pp. 91–94.
5 William Gudenrath and David Whitehouse, “The Manufacture of the [Portland] Vase and Its Ancient Repair,” Journal of Glass Studies, v. 32, 1990, p. 109, fig. 66.
6 Rosemarie Lierke, Antike Glastopferei: Ein vergessenes Kapitel der Glasgeschichte, Mainz am Rhein: Philipp von Zabern, 1999, pp. 118–129.
7 A. John Gwinnett and Leonard Gorelick, “An Innovative Method to Investigate the Technique of Finishing an Ancient Glass Artifact,” Journal of Glass Studies, v. 25, 1983, pp. 249– 256.
8 Josef Welzel, “Becher aus Flechtwerk von Kristall”: Diatretglaser, ihre Geschichte und Schleiftechnik, Hadamar: Verein der Freunde und Forderer der Erwin-Stein-Schule Staatliche Glasfachschule Hadamar, 1994; idem, “Antwort auf Fragen von Rosemarie Lierke,” Journal of Glass Studies, v. 45, 2003, pp. 186–189.
9 George D. Scott, “A Study of the Lycurgus Cup,” Journal of Glass Studies, v. 37, 1995, pp. 51–64.
10 Brill [note 1], v. 1, pp. 79–80, and v. 2, p. 146; Freestone and others [note 1]; Robert H. Brill, “The Scientific Investigation of Ancient Glasses,” Proceedings of the VIIIth International Congress on Glass, London, Sheffield: The Society of Glass Technology, 1968, pp. 47–68.
11 Harden and Toynbee [note 1]; Freestone and others [note 1].
12 Harden and Toynbee [note 1], p. 205, no. A6; David Whitehouse, “Fragments of Late Roman Cage Cups in the United States,” Annales de l’Association Internationale pour l’Histoire du Verre, v. 12, Vienna, 1991 (Amsterdam, 1993), pp. 111–119, esp. pp. 112–113, no. 1.
13 Harden and Toynbee [note 1], p. 210, no. B11.
14 Brill [note 1], v. 1, p. 80, and v. 2, p. 146, no. 3802.
15 78.1.17: Whitehouse [note 12], pp. 113–115, no. 2; idem, Roman Glass in The Corning Museum of Glass, Volume One, 1997, pp. 286–287, no. 481; Brill [note 1], v. 1, p. 80, and v. 2, p. 146, no. 3390.
16 Constanze Hopken, “A Fragment of a Dichroic Cage Cup from Duluk Baba Tepesi / Doliche, Turkey,” Journal of Glass Studies, v. 50, 2008, pp. 303–306.
17 Harden and Toynbee [note 1], p. 209, no. B6; Harden and others [note 2], p. 239, no. 134; Elisabetta Roffia, I vetri antichi delle Civiche raccolte archeologiche di Milano, Milan: Comune di Milano, 1993, pp. 184–197, no. 401.
18 This is seen most clearly in Roffia [note 17], p. 196.
19 Harden and Toynbee [note 1], p. 205, no. A5.
20 Ibid., p. 210, no. B8.
21 Harden and others [note 2], pp. 229–230, no. 128.
Published on January 21, 2013