Gold glass or gold sandwich glass is a luxury form of glass where a decorative design in gold leaf is fused between two layers of glass. First found in Hellenistic Greece, it is especially characteristic of the Roman glass of the Late Empire in the 3rd and 4th century AD, where the gold decorated roundels of cups and other vessels were often cut out of the piece they had originally decorated and cemented to the walls of the catacombs of Rome as grave markers for the small recesses where bodies were buried. About 500 pieces of gold glass used in this way have been recovered.Grig, 204-5; Lutraan, iii and 2 (note also); 8–9 Corning video Complete vessels are far rarer. Many show religious imagery from Christianity, traditional Greco-Roman religion and its various cultic developments, and in a few examples Judaism. Others show portraits of their owners, and the finest are "among the most vivid portraits to survive from Early Christian times. They stare out at us with an extraordinary stern and melancholy intensity".Honour and Fleming, Pt 2, "The Catacombs" at illustration 7.7 From the 1st century AD the technique was also used for the gold colour in mosaics.
Various different techniques may sometimes also be described as "gold glass". Zwischengoldglas is very similar but the two layers of glass are cemented, not fused. It mostly comes from Germany and Bohemia from the 18th and 19th centuries. Verre églomisé properly covers a single layer of glass which is gilded (or coated with other types of metal leaf) on the back, as used in 19th century shop signs and the like. One process was revived by Jean-Baptise Glomy (1711–1786), hence the name. Both of these processes were also used in ancient times, and the German and French languages often use their native terms for what is called "gold glass" in English. Gold ruby glass or "cranberry glass" is actually red, coloured by the addition of gold oxide.See the Corning Museum "Glass glossary" entries for all these terms Gold-band glass is another ancient technique covered below.
Technique The manufacturing process for gold glass was difficult and required great skill. For a Late Roman glass, first a small round flat disc, typically about across, was cut away from a blown sphere with a flattened bottom, either made of coloured or plain glass. A piece of gold leaf was then glued to this with gum arabic. The design was created by scraping away gold leaf. The main vessel, a cup or bowl, was formed by blowing and cutting, with a flat bottom the same size as the first disc. This was then heated again and carefully lowered onto the disc with the design, superimposing the flat bottom with the disc with the design so that they fused together. The complete vessel was then heated a final time to complete the fusing. Different accounts of different periods vary somewhat as to the precise sequence of stages and other details, but the process is essentially the same.Corning video; see also the Corning Museum "Glass glossary", which appears to somewhat contradict the video.
The larger Hellenistic glass bowls are thought to have been formed using moulding rather than blown, as the whole bowl is doubled and the inner and outer vessels must fit together exactly.Williams, 190 Some of the finer later medallions seem to have been made as such from the start, and some contain pigments other than the gold.Example from the Corning Museum of Glass showing both features; also Gennadios and the Brescia portrait These smoother-edged medallions exploited the medium of glass as a matrix for portrait miniatures, and it has proved to be a very effective one, outlasting all alternatives except for precious metal and engraved gems. They were probably initially made to be hung for display, or set in jewellery in smaller examples like that of Gennadios, but were also used for funerary purposes, and often use a base of blue glass. They are a few Roman examples of vessels from Cologne of a different style where several of what have been called "sidewall blobs", small gold glass medallions about across, with images, are fused into the walls of a vessel.Grig, 204; Lutraan, 3–4 and note, now British Museum; Vickers, 612–613 has the best photos of "blobs"
Apart from roundels with figurative images the fused sandwich technique was used to create the tesserae for gold in mosaics, and for beads and the like. Gold glass tesserae, at least by Byzantine times, had a very thin top layer of glass, which was probably poured onto the lower glass with the gold leaf glued to it. Tesserae were made in blocks or "cakes" and then cut into cubes, which are relatively large in the case of gold backgrounds. Gold backgrounds were laid over earth red or yellow ochre backgrounds which enhanced their visual effect. Most colours of tesserae seem to have been made locally to the mosaic, but there is some discussion as to whether this was true for gold glass ones. In the 11th century the relatively new Christian centre of Kiev seems to have used gold tesserae made in Constantinople.Cormack, 388–391; Grove, 124
Roman gold glass beads were made by using an inner tube or rod to which the gold leaf was stuck. A larger tube was slid over that and the beads crimped off. Easily transported and very attractive, Roman gold glass beads have been found as far outside the Empire as the Wari-Bateshwar ruins in Bangladesh, and sites in China, Korea, Thailand and Malaysia.Francis, 91–93
Gold-band glass is a related Hellenistic and Roman technique, where strips of gold leaf, sandwiched between colourless glass, are used as part of the marbling effect in onyx glass. It is mostly found in small perfume bottles and the like.Trentinella, Rosemarie. "Roman Gold-Band Glass", Heilbrunn Timeline of Art History, New York: The Metropolitan Museum of Art, 2003
Grave-markers
The most common form of vessel in late Roman examples was a bowl or drinking cup, which are thought to have been originally family gifts for weddings, anniversaries, New Year, the various religious festivals and the like, in some cases perhaps presented at birth or Christian baptism.Beckwith, 25; Weitzmann no. 396; Rudgers, 85 None of the type of gold glass vessels cut down as grave-markers has survived complete, though about 500 of the cut-off bottoms are known,Grig, 204; Lutraan, iii and 2 (note also), 8–9 but since so many have inscriptions encouraging the owner to drink, they are usually referred to as "cups" or "glasses". However Roman drinking cups and glasses were often very wide and shallow, though tall straight-sided or slightly flared shapes like modern tumblers are also found. A mosaic in the North African ruins of Dougga shows two hefty slaves pouring wine from amphorae into two shallow bowls held by slaves waiting on the banquet. The two amphorae are inscribed with "ΠΙΕ" and "ΣΗϹΗϹ" the Greek originals of the toasting formulae "" ("Drink, may you live", discussed below) so common on Roman glasses, and it has been suggested that the mosaic shows the shape a complete cup would have had.by Smith, see Lutraan, 75 and note 197
At what was probably a much later date, perhaps after decades of use, on the death of the owner the main vessel of undecorated glass was cut away and trimmed to leave only the gold glass roundel, which was then used in the catacombs as a grave marker. Presumably in many cases the cup had already broken in the normal course of use, and the thick bottom with the decoration had been preserved for later use in this way. Bodies were buried in the catacombs in small recesses called loculi, stacked one above another mostly along narrow corridors hollowed out from the soft rock, and no doubt some form of marker was necessary for visitors to locate the right spot. They may also have functioned as a seal on the grave, as they were pressed into the mortar or stucco forming the final surface of the wall of the loculus; other classes of small decorative objects were also used in the same way. They may also have been regarded as capable of warding off evil spirits, especially in the later part of the period, when portraits of saints become most common.Rutgers, 84–85; Grig, 204–209, and throughout; Beckwith, 25; Honour and Fleming, Pt 2, "The Catacombs" at illustration 7.6; Lutraan, 4–5
The very untidy trimming of many examples may be explained by this; an example in the Metropolitan Museum of Art is still attached to a chunk of mortar round much of its edge, showing that the mortar overlapped the edge of the glass. Rough edges would mostly have been hidden by the mortar and also provided a firmer key for the mortar to hold the glass in place (as it happens the edges of the New York piece are unusually neatly trimmed).Bowl Base with Christ Giving Martyrs’ Crowns to Saints Peter and Paul, MMA online, accn. 11.91.4; see also Lutraan, 5 and note 7
Many pieces of gold glass had portraits of private individuals, mostly married couples, who may have included the deceased, while others had portraits of religious figures such as saints, or religious symbols. This custom was followed by Christian, Jewish (13 identifiably Jewish examples are known) and pagan Romans. The different sets of imagery, apart from the increased number of private portraits, are typical of the paintings also found in the catacombs and other Early Christian art and its Jewish equivalent from the period.Beckwith, 25–26; For Jewish material, Rudgers, 81–85 (13 examples on 81); Weitzmann p. 371 and numbers 347 ff.; Lutraan, 12 and throughout As Christian art developed in the late 4th and 5th centuries, its changes are reflected in the subjects and their treatment in gold glass, before the catacombs ceased to be used and the supply of examples ends.Weitzmann nos. 503, 507–8, 510 are late examples
Hellenistic period The technique was used in Hellenistic times, and Hellenistic examples are generally both more technically ambitious than Roman ones, with wide bowls or drinking cups decorated all round their curved sides in gold glass, and executed with more artistry.Gold-glass skyphos (drinking cup) fragment, Metropolitan Museum of Art (23.160.76) The British Museum has a virtually complete bowl (broken but repaired) 19.3 cm wide and 11.4 cm high, one of two from a tomb in Canosa in Apulia dating to around 270–160 BC. It has most of the interior very finely decorated with lotus and acanthus motifs, which are more typical of gold glass in this period than designs with human figures. There are a handful of other near complete examples, and rather more fragments.Rotroff, 333
These pieces are usually assigned to Alexandria in Egypt, which is often seen as the originating centre for luxury Hellenistic glass, and is mentioned as the source of over-elaborate glass by the 1st century satirist Martial and other sources; one seems to show a Nilotic landscape, though this was a popular subject elsewhere. However fragments have been found when excavating a glass factory on Rhodes. A description perhaps dating from the 270s BC (surviving in the works of the later writer Athenaeus) mentions two vessels that are diachysa ("with gold in it") and very likely made by this technique."Sandwich gold-glass bowl", British Museum online highlights; Williams, 190. Though textually very similar, these differ over the dating, with the book (2009) saying 210–160 BC and the website (in May 2013) 270–200 BC. Further photos here
Roman period
Gold glass mosaic tesserae begin to be used in domestic mosaics in the 1st century AD, with Rome apparently the first location. They continued to be used throughout the ancient and medieval periods into the modern day. By around 400 gold began to be used as the background colour for Christian religious mosaics, as it was throughout the Byzantine period.Conventi, 1–3; specifically, "the earliest known use of gold tesserae was in 55 AD, in the Gardens of Lucullus by the Spanish Steps in Rome