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Rosemarie Lierke
Antike Glastechnologie / Ancient Glass Technology
Cameo glass
What kind of manufacturing traces are visible, how can they be explained?
Text I. Cameo glass - more evidence of molding (with a supplement)
Text II. How about an earlier date for some cameo glasses?
see also about cameo glass: L1996a (many detail photographs); L1997b (short article in Annals AIHV); Lierke/Lindig 1997 (cameo technique, first investigation of the internal scratches); Mommsen 1997 in Glass Sci. Technol. 70, 1997, No. 7, 211-219 (X-ray fluorescence analyses); L1999 (the book ‘Antike Glastöpferei’, see especially the chapter on cameo glass); L2002b (scientific investigation of the internal scratches and a fused on trail); L2004a (contribution to a discussion in ‘Minerva’). On this website: English summary of L1999, Glass pottery / small supplement concerning cameo glass.
Hot forming of cameo glass - the principle
model plaster mold powder-filled hot glass pressing sagging rim flows rim narrowed cooled
One of the most important results of many years of investigations was to learn that the early Roman
cameo glasses were not cut from a blank with two differently colored glass layers. Instead, they were most probably formed hot, using glass powder for the cameo decor which melts from the heat
of the glowing hot body glass. The process is related to the manufacturing process of Terra Sigillata - using easily crumbling one-time plaster molds instead of reusable ceramic molds.
The hot forming of cameo glass contradicts the ruling opinion which prefers to consider the cameo glass vessels as ‘masterpieces of the art of glass cutting of all times’. But, the decision between the
different opinions is not a question of believing or not believing, it is a question of a sober evaluation of controllable facts. Everybody interested may have a closer look at the originals and make up his
own mind from their manufacturing marks.
What kind of manufacturing traces are visible, how can they be explained?
Some features of the two impressive cameo vessels in the British Museum, the Auldjo Jug (GR 1840.12-15.41), and the Portland Vase (GR 1945.9-27.1) are mentioned here. These features can
easily be detected by an attentive visitor of the museum. 
The Auldjo Jug: 1. The handle is connected - not applied
- to the vessel at its upper end. Handle and vessel are one piece of glass (this was confirmed by M. Bimson in D.B. Harden JGS 23, 1983, 51). What does this mean? The
vessel and the handle are obviously formed at the same time. The handle was not applied subsequently as is customary with blown glass. It was cut or pressed from a one-sided much
longer neck. This is supported also by the obviously pressed - not cut - pattern on the handle. At its lower end, the handle was applied with some hot glass to the already existing decor. This decor was not cut later.
2. 3. The white ring with rounded surface around the middle of the vessel is wavy (see above right). What does this mean?
A ring cut from a cold cutting blank would be traced on the blank first, and therefore be level and straight. A cut ring would most probably not have a rounded surface, since
any rounded protruding feature must be ‘modeled’ with innumerous tiny cutting facets. This requires a tremendeous amount of work. Obviously, the ring was molded and it became wavy while the glass was still hot. 4
. Where the tendrils lost their white decor, 
The wall with decor was deformed from the application of the handle. What does this mean? As
indicated by the drawing (left), this deformation seems to have been caused by the weight of the handle while the vessel was positioned upside-down on a mushroom- shaped plaster support during the final manufacturing process. [see
the dark glass underneath becomes visible with a
rounded protruding profile - and, the same is true for the partly visible cross section of a leaf beside an insert (see arrow right). The dark glass can be recognized to intrude into the white glass. What does this mean?
A two-layered blown cutting blank would always show an even interface between the two layers. The dark glass would never intrude into any bulge of the white glass. The Auldjo Jug therefore
was not made from an overlay (two-layered) blank.
Supplement: occasionally it is theorized that the blanks of the cameo glasses are two-layered mold blown. This is perfect nonsense. No single cameo glass - it may be thin- or thick-walled - shows the slightest relief on its inside as would be expected at any mold blown glass.
The Portland Vase
: Only few manufacturing traces are visible at the Portland Vase, because of its history of several restorations. It bears now a
high gloss polish which is without comparison, and which probably was caused by an earlier restoration. The few traces, however, are sufficient to preclude a cutting of the cameo decor. 1
. It is striking that the horns at the lower attachments of the handles remained uncut. This was firstly described by 2. No defects caused by grinding or cutting are visible, however, modelling flaws could be discerned. For an example see text I, 3
. To the right side of this foot are slightly slanting and extremely vertically stretched bubbles visible in the dark glass, while the bubbles nearby in the white glass of the vessel are nearly round. What does this mean?
In a two-layered blown cutting blank, the bubbles in both layers should have about the same deformation or none. This means again, the Portland Vase was not made from a two-layered cutting blank [see also Text I.1].
Both cameo vessels - as a matter of fact all early cameo vessels - have no cameo decor at the
handles, at the neck or at the rim. Not visible to a visitor are the typical traces on the inside of these vessels which are significant for the manufacturing process. In the literature, the traces are
seldom mentioned and - if mentioned - so far not correctly explained (Portland Vase: occasionally mentioned as ‘grinding marks’, correct would be ‘rotary scratches’, see text I,1; Auldjo Jug: vertical
traces in the neck mentioned as ‘blowing striations’(unparalleled in other blown vessels!), better would be ‘flowing striations’ [L1996a, Abb. 3; 31; Harden JGS 25, 1983; see also here (reference
to p.623)]. The internal traces distinguish the two vessels - as well as all other early cameo glasses - from blown glass. All manufacturing traces which have been mentioned here could be explained by
hot-forming of the cameo glasses as shown above. In cooperation with scholars of different scientific background, the problem of the cameo glass manufacturing was thoroughly investigated. The support of the Deutsche Forschungsgemeinschaft
enabled investigations of original vessels and fragments and some
A special thank is addressed to all who made it possible - despite a different opinion - to investigate original
vessels and fragments in their care. Some cameo plates, 12 cameo vessels and about 200 fragments exist. Thereof 6 vessels, 2 plates and numerous fragments were privately investigated. My thank is dedicated especially to the
British Museum for several investigations (Dr. V. Tatton- Brown and Dr. Paul Roberts). Last update January 19, 2007
The following text (here with few additions) was presented as part of a poster at the 15th congress of the AIHV, New York/ Corning Oct. 15-20, 2001, but a summary of the poster texts was not printed in the Annals. If you like to make citations, please mention author, congress and web site with date.
I
Cameo glass – more evidence of molding
A close-up investigation of early Roman cameo glass rendered many arguments in favor of a manufacture without cutting. Insurmountable doubts were raised that stress-free overlay cutting
blanks could have been blown - just one or two generations after the invention of glass blowing. It also seemed very unlikely, that all-time masterpieces of relief cutting could be made at least half a
century before simple intaglio facet cutting was firstly tried. Many discussions in the meantime have added to the evidence of molding. 1. Elongated bubbles
in the blue glass were mentioned as proof that the blank of the Portland Vase was blown [W. Gudenrath and D. Whitehouse, The manufacture of the vase and its ancient repair, J.
Glass Studies 32, 1990, p. 109, Fig. 67, showing lower part of right leg with foot of seated female figure and vertically stretched bubbles in the neighboring blue background]. However, in the lower
wall area of a vessel, the bubble distortion is about the same whether this vessel was blown and stretched or pressed. Something else is important: Since the two layers of an overlay glass are blown
together, bubbles in both layers should endure about the same distortion. In our case: if the Vase was blown and the bubbles in the blue glass are elongated, the bubbles in the white glass should be
elongated about the same. But, the bubbles in the white glass in the same area are round. This is best to be checked at the original vase, but it is visible also on the photo mentioned above. This feature
was not regarded yet, but it is easily explained by the proposed molding process [see The white glass powder is held in the cavities of a plaster mold while the blue glass is pressed as
very hot lump into this mold. The white glass will melt from the heat, but not move from its place. Therefore, bubbles in the blue glass may get stretched, but the bubbles in the white glass will remain
round. Plaster molds do not stick to the glass and crumble easily after enduring the contact with the hot glass. 2. The right foot [of the seated figure mentioned above, here shown as a detail from the front cover
of
3. Typically, the inside of early Roman cameo glass is wholly or partially covered with rotary scratches
. It was assumed that the cause of these horizontal striations on the inside of the Portland Vase was ‘internal grinding’ to test for or to remove stress [W. Gudenrath and D. Whitehouse, The
internal grinding of the vase, J. Glass Studies 32, 1990, p.137]. Because this opinion is still occasionally cited, I shortly repeat an earlier reply [
Supplement: In the meantime appeared: Ursula Liepmann, Ein augusteisches Kameoglas im Kestner-Museum zu Hannover. Niederdeutsche Beiträge zur Kunstgeschichte Bd. 41 (2002) S. 9 – 36. With detailed technological, stylistic and chronological considerations and investigations, an object from the collection of August Kestner is presented. Here as supplement to the text above, a feature shell be mentioned which is known from other examples as well: the relief proceeding into the dark background. The cameo fragment from Hannover shows two male figures, one of them with a comparatively flat hair-do. A close-up view reveals that the hair-do is partly in dark relief. This detail hardly could be explained here as intentional stylistic feature with a mystical effect, showing the superior quality of the glass cutting - as was done concerning other examples. By hot-forming, such a feature appears - with or without intention - if a cavity in the mold was not filled with enough white glass powder to cover the dark background after melting. [see the illustration of a small experimental cameo plate Glass pottery / illustrations f]. U. Liepmann shares this last explanation. She also found other details in agreement with the hot-forming of this object. R. Lierke, August 13, 2003
The following text (here with few additions) was presented as part of a poster at the 15th congress of the AIHV, New York/ Corning Oct. 15-20, 2001, but a summary of the poster texts was not printed in the Annals. If you like to make citations, please mention author, congress and web site with date.
II
How about an earlier date for some cameo glasses? Molded relief ornaments of Egyptian faience or glass were known at least since the 18th
dynasty in Egypt. Faience was made from powdered constituents, while glass was either sintered from glass powder or pressed from reheated chunks of raw glass. In Ptolemaic times, the molded glass inlays
became quite sophisticated. No wonder that the first cut cameo stones became an inspiration for this art too. Several three-layered glass cameo portraits of Ptolemaic kings are known, dated early 2nd/ first half 1st
c. BC [D. Plantzos, Ptolemaic cameos of the second and first centuries B.C., Oxford Journal of Archaeology, v. 15, no. 1, 1996, pp. 39-61]. There is hardly any doubt that these were
made in the tradition of the just mentioned molded relief ornaments. Their appearance equals other three-layered molded glass cameos. The use of glass powder for the cameo decor was confirmed
for those – fully in agreement with independent investigations by C. Weiß [see Lierke in A little detour leads to cameo glass vessels. Closed ‘onyx’ or ‘banded’ glasses without remarkable
traces of a core exist probably since the 2nd c. BC already. However, the small glass tubes used for blowing the first tiny and thin-walled glasses in the 2nd half of 1st c. BC could never be used to pick
up and inflate a thick-walled prefabricated blank for an onyx glass vessel. The first sturdy metal blow tubes obviously were not used earlier than in the second half of the 1st c. AD for cinerary urns. The
onyx glass vessels and the well known gold-band bottles among others are proof, that it was possible to produce hollow vessels without blowing. Both vessel types occasionally feature internal
‘flowing striations’ in the neck - which are also known from some cameo glasses, but unknown from blown glass. [
In any case, the technological preconditions to make cameo vessels were given already before the last quarter of the 1st c. BC. It was possible to mold glass cameos, and it was possible to make
hollow vessels without blowing and without adhering core. Both abilities had to be combined. The few extant ‘early Roman’ cameo glass vessels are all dated today late 1st c. BC/first half 1st c. AD.
Only the Corning cameo lagynos no. 68.1.1 (assumed origin: the eastern Mediterranean), was indeed cautiously assigned by A. Oliver to late 2nd /1st c. BC [A. Oliver Jr., Glass Lagynoi, Journal
of Glass Studies, v.14, 1972, pp. 17-22]. Its numerous ceramic parallels are dated 3rd/1st c. BC. Searching for ceramic parallels for other cameo glasses brings astonishing results. The bottom rosette
of the small bottle in the Getty Museum (a), said to be from Eskisehir/Turkey, almost fits into a mold fragment from Kyme near Izmir (b) which was dated by J. Bouzek to about the 2nd quarter 2nd c.
BC. It resembles many rosettes from ‘Megarian bowls’ (2nd c./first half 1st c. BC), see the examples c, d. The latter applies as well to the 8-pointed star rosette of the Morgan cup in the
Corning Museum (e) which is said to be from the Turkish Black Sea coast - see examples f, g, dated 145-100 BC, or 2nd/3rd quarter of 2nd c. BC. The cameo glasses were not necessarily made at the
same date as the ceramic vessels with comparable decor elements, but the possibility is suggested that some cameo glasses may be older than previously thought. Bottom rosettes of ceramic vessels
do not occur after the Megarian bowls.
Bottom rosettes of cameo glass vessels (a and e) and relief ceramic bowls # a) cameo balsamarium, last quarter 1st c. BC/1st quarter 1st c. AD, Paul Getty Museum
acc. no. 85 AF 84 (D.B.Harden et al. Glass of the Ceasars 1987, p. 83-84, photo courtesy museum). # b) ceramic mould fragment, 2nd/3rd quarter 2nd c. BC (J. Bouzek, Anatolian coll. of Charles Univ. 1974, pl.2/14. # c
) Megarian bowl, 1st half 2nd c. BC (G. de Luca, W. Radt, Sondagen im Fundament des Altars, Pergamenische Forschungen v. 12, 1999, Beilage 13/530). # d) Megarian bowl (Bouzek, cp. b), pl. 5/25). # e
) Cameo bowl, 1st half 1st c. AD, Corning Museum of Glass acc. no. 51.1993 (D. Whitehouse, Roman Glass in the Corning Museum of Glass, v. 1, 1997, p. 48-51). The same vessel was dated by E. Simon: ‘3rd quarter
of the 1st c. BC or earlier’ (J. Glass Studies v. 6, 1964, pp 13-30). # f) Megarian bowl, dated 145-100BC (S. Rotroff, Hellenistic Pottery: Athenian and Imported Moldmade Bowls, The Athenian Agora, ASCSA 1982, pl. 87/322). #
g) Megarian bowl, ~1st half 2nd c. BC (Bouzek cp. b), pl. 7/44). # h ) Megarian bowl, 2nd or 3rd quarter 2nd c. BC, Nationalmuseum Athens,
acc. no. 14624 (U. Hausmann, Hellenistische Reliefbecher aus attischen und böotischen Werkstätten, 1959, ppl. 37/2)
It is striking also that all cameo glasses and all ceramic parallels mentioned so far, have or are assumed to have an eastern origin. The same is true for two more cameo vessels, a skyphos or
rather goblet kantharos in the Getty Museum, which is said to be from a Parthian tomb in Iran, and is dated last quarter 1st c. BC/1st quarter 1st c. AD [in Harden et al., Glass of the Caesars 1987, p.
68 ], and in addition a small vessel of the same type [see the
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.