D   Home Publikationen G lastöpferei Techniken Kameoglas Diatretglas Hedwigsbecher Craqueléglas Werdegang  D

E English Home Publications G lass Pottery Techniques Cameo Glass Cage Cups H edwig Beakers Craquele Vita E

Rosemarie Lierke

Antike Glastechnologie / Ancient Glass Technology

Ancient Glass Pottery

See also English summary of ‘Antike Glastöpferei’                                                                

Where does the term ‘glass pottery’ come from?

What are the basic working methods of glass pottery?

When and where was glass pottery practiced?

The history of research (with: Small supplement concerning cameo glass)

Own glass pottery experiments (with link to some illustrations)

Supplement 1: Archaeological glass experiments – no simple matter

Supplement 2: Concerning recent replicas of reticella and ribbed bowls

Controversies

Where does the term ‘glass pottery’ come from?

Perhaps, some people do not like that a rare and noble material like the early glass is mentioned together with ‘ordinary’ pottery. However, in a technologically oriented context, it is justified and advantageous to talk about ‘glass pottery’. Glass is an offspring of ceramics and the term ‘glass pottery is suited to visualize this technological and chronological relationship.

While the first independent proper glass material seems to have become known as slag from copper smelting, the potters already knew this material as glaze since centuries.

From the glass constituents silica, soda and lime - in somewhat different proportions than for glass - the potters used to make the ‘Egyptian faience’. During the firing of this siliceous ceramics, the soda was enriched in the surface and caused a glossy layer which was nothing else but glass.

The new material glass was used and processed in pottery workshops. Pottery methods were adapted and applied to the glass, and pottery shapes were the models for the early glass vessels.

If the new material really was developed as a ‘by-product’ of copper smelting, it does make sense to assume that the very first raw glass chunks and ingots were made around the middle of the third millennium by specialized metal founders and were delivered to other workshops. Glass could not be worked like metal. Casting (pouring) of glass (comparable to metal) was not possible since the high temperatures and special crucibles required were not available yet [W.E.S. Turner, J. Soc. Glass Technology 38 (1954) 436T-444T]. They became avaiable only in more recent times. Working big chunks of raw glass by cutting (comparble to stone) was almost impossible because of the unsolved strain problems [L2003b]. Therefore, neither metal nor stone workshops were adapted to the manufacture of glass vessels.

Glass blowing appeared in the middle of the first century BC. It was the first working method peculiar to the material glass, which also produced the first genuine glass vessel shapes,

What are the basic working methods of glass pottery?

All early glass working methods before glass blowing are related to pottery methods [L1999, 24].

Sintering. Comparable to the making of Egyptian faience, glass powder and/or glass particles were layered into a mold or over a removable core. The glass powder was fired (sintered) in a kiln or in a forced fire. This process may have been repeated.

This way also the first cored vessels were made. The core was not dipped into or trailed with molten glass (trailing or winding was used later for vessels). For the decor only, reheated glass rods were wound around the vessel. 

Winding. The raw glass was reheated and the viscous mass drawn as rods to be worked later, or directly trailed around a removable core. Winding, too, is an early pottery method (usually without core).

The winding method was used from the beginning of glass working for bead making, later for decorating vessels, and finally for the making of vessels - for instance the cored vessels of the first millennium BC.

Pressing. Just like clay was pressed into patterned molds for the relief ceramics, the viscous glass was pressed - with or without relief - into or over molds. Stationary or rotary pressing was one of the most important methods of early glass working.

The ancient glass pressing was no mass production. Relief-ceramic vessels shrink during the drying, and therefore can be taken out of their reusable mold before firing. This does not apply to glass. Pressed glass today is made in multi-part molds which can be used over and over again. Unlike these examples, ancient glass vessels with relief were pressed in one-part plaster molds which were not reusable. The plaster lost its bond from the contact with the hot glass. But, the plaster mold therefore could easily be taken off, even before the cooling, and the vessel could still be worked on or become fire-polished. Plaster of Paris or mixtures of plaster and quartz powder are especially suited as molds since they contain humidity and do not stick to the glass (plaster cannot become glazed!).

The pressing of glass became more sophisticated through the centuries, for instance for the cameo glasses or the double shelled blanks of cage cups.

The typical rotary scratches of ancient glasses (so far erroneously taken to be grinding marks [L2002b]) indicate a turning of the mold during the pressing - like ceramics. The hot glass this way was more easily distributed and any danger of sticking more easily avoided.

For glass working, a fast turning wheel was not required. Mostly, only a few revolutions of the wheel were required, for instance two revolutions for the making of a ribbed bowl. As a rule, a simple turntable was sufficient.

Sagging. Open bowls could be made by sagging a prefabricated disk of glass into or over a mold, for instance mosaic bowls, or by the natural flowing of a hot glass cake over a core. Sagging over a mushroom-shaped core and pressing the flowing glass close to the stem led to the making of hollow vessels, for instance a cameo bottle.

 In case the core contained some moisture, the hollow vessel by skillful manipulation (closing the neck tight against the core) could become inflated by steam. This way, the two types of gold-band vessels were generated, without or with inflation [L1999, fig. 163, 164]. In each case, the plaster core became brittle from the heat and could easily be removed. The hollow vessels which were made by sagging and steaming were the immediate predecessors of blown glass. However, unlike blown glass, they show usually distinct manufacturing marks on their inside: e. g. horizontal scratches in the corpus region, or flowing marks in the neck, or traces of the core.

Sintering, winding, pressing and sagging are the basic working methods of glass pottery. They were used in many different variations and combinations. 

When and where was glass pottery practiced?

Up to the invention of glass blowing, the glass working in all glass working centers was based on the glass pottery methods. The climax was reached within the last years BC with the ‘pottered’ hollow glasses, especially with the terrific cameo glasses - which were demanding objects concerning not only their art but also their manufacturing process.

It is not really known yet, where the first cameo glasses were made [see Cameo glass/Text II].

In the first half of the second century the glass pottery came to a preliminary end, at least in the well-known glass centers in the middle of Europe.

After the invention of glass blowing - probably  made possible by a new type of glass furnace - the glass vessel production was enormously intensified. The ribbed bowls only could easily compete with blown glass for over hundred years. They were fastly produced on the wheel and were very well suited for usage. Most other glass pottery products slowly disappeared from the market.  In the second half of the first century AD the popular mass-produced mold-blown vessels of the glass blowers competed against the rare high relief glasses of the glass potters which were pressed each single one in a lost mold. A last success of the glass potters were the cutting blanks for facet beakers and other early cut glasses (recognizable from the single or double protruding rings around the rim or further down, and a central round protrusion in the bottom). However, soon even the blanks of facet beakers were blown (recognizable from the missing rings, usually replaced by cut grooves, and often by a cracked off rim, which sometimes was ground smooth). 

It is not known yet where the glass pottery survived til its later revival. Since the 3rd century appear rotary pressed (‘pottered’) relief glasses of a superb quality, concerning both art and technique. One would assume that only a continuous development could bring about such a progress. To these glasses belong the relief skyphoi which were found in the Rhineland [L1995a; L1999, 266ff], or later the cage cups, some of which were found in Southeastern Europe or the Eastern Mediterranean region [a list of the cage cups which were known til 1995 in L1995c, 267/68].

Some particular types of glasses support the idea of a continuation of glass pottery for Sasanian and Islamic glass. These glasses perhaps were the inspiration for the special production technique of the medieval Hedwig beakers [Techniques/ Hedwig beakers; L2005]. However, the manufacturing technique of the Hedwig beakers could as well be a genuine re-invention of a glass pottery method since it was very well suited to use reheated raw glass for the making of just one single vessel at a time. As a curiosity, a re-invention of glass pottery took also place under somewhat different preconditions in the twentieth century [L1995a, 42 or L1999, 26, or L2004c].

The history of research

The erroneous interpretation of the frequent internal rotary scratches of ancient glass as grinding marks often blurred the realistic perception of ancient glass working. It was assumed that mold-formed vessels, assumedly including the widespread ribbed bowls, generally were ground on their inside. The erroneous interpretation of the scratches caused in addition a tremendous overestimation of the ancient art of glass cutting, and it caused the unrealistic assumption that it was possible in antiquity to make glass vessels from raw glass or from a blank which was fixed to a lathe and turned [L2002b, L2004c]. However, again and again, some scholars cautiously claimed exceptions or alternatives to the traditional explanations after the investigation of certain originals.

Two female archaeologists have to be mentioned especially. The American Gladys D. Weinberg called the rather irregular early specimen of ribbed bowls ‘tool-ribbed’ – a term which in reality best describes all ribbed bowls, even the perfectly made late ones [J. Glass Studies 15 (1973) 35-51]. Her German colleague T. E. Haevernick noticed that a turning motion was involved during the making of ribbed bowls [J. Glass Studies 17 (1975) 71-73]. Both observations together, checked against hundreds of bowls or fragments thereof from the whole production time of these vessels, led to the explanation given here for the manufacturing technique of ribbed bowls.

For cameo glass shall be mentioned only Gustavus A. Eisen and Fahim Kouchakji. They proposed 1927 in their well-known book ‘Glass, its origin, history, chronology, technic and classification to the sixteenth century’ the hot-forming of cameo glass as a possible alternative to the cutting theory. Hans Jucker mentions 1965 two cameo fragments which were in his opinion not cut [Antike Kunst 8 (1965) 40-54].

In the fiftieth and sixtieth of the last century already, T. E. Haevernick opposed the theory of F. Fremersdorf, who claimed that cage cups were cut from a thick-walled blank. In a letter from 13.2.1959 to Dr. Mayer, Glasfachschule Zwiesel, she describes for the first time the idea of using an intermediate ‘device’ during the hot-forming of the cage cup blanks. She was thinking of something made from wood which would not have worked, but the perforated plaster beaker which was verified to serve the purpose, is like a final realization of her idea. T. E. Haevernick was also the first, who went through tremendous trouble to initiate scientific investigations [H. Hannes, in: Techn. Beiträge Arch., 1959, 78-80] of a small cage cup fragment. She always used to regret that practical experiments to investigate ancient manufacturing methods were not accessible to her.

Today, many studio-glass workshops offer the possibility to learn something about the working with hot glass. The first archaeologist to use such an opportunity consistently and successfully, was E. Marianne Stern in the studio-glass workshop of the Toledo Museum of Art. With her practical experience, she was able to make important observations about possible technological methods in antiquity. When the Portland Vase was taken apart for restoration in 1989 she noticed from the internal traces that this vessel was not blown (oral communication). Her archaeological publications are distinguished by systematical investigations of manufacturing traces and consequently detailed descriptions of ancient objects. They always provide an insight into the ancient manufacturing techniques. For an experimental investigation of the manufacturing methods of cored vessels, she cooperated with the studio-glass artist Dudley Giberson. He provided the convincing reconstruction of an ancient furnace which permitted the working of raw glass without crucibles [The Volcano Dream, GAS J. 1995, 77-84]. With this furnace it was possible to work at one glass vessel directly in the fire. Giberson’s furnace with great probability matches the furnace of a small workshop in antiquity were the imported raw glass was worked.

Almost all the co-authors of the book ‚Antike Glastöpferei – ein vergessenes Kapitel der Glasgeschichte’ (Ancient glass pottery - a forgotten chapter of glass history), who are mentioned in the following, were known in their special field for own results which are in agreement with the new perception of ancient glass working or with the consequences thereof.

Albrecht Locher confirmed as philologist, that the Plinius quotation ‘aliud torno teritur’ is in agreement with the perception of rotary pressed glass, that it does not mean rotary ground glass.

The glass technologist Matthias R. Lindig recognized the ancient scratches to be a known production defect of hot glass which is caused by tiny blemishes or protrusions in the mold or tool material. This defect occurs still today and is easily identified. In antiquity, it seems to have been almost unavoidable.

Birgit Schlick-Nolte, an Egyptologist and known glass expert, always has paid special attention to technical details. She added her universal knowledge about the early glass history. Her contribution illuminated the continuity and logic in the development of early glass-working.

The work of E. Marianne Stern was mentioned already. In her contribution to the ‚Antike Glastöpferei’ she investigated the mutual influence of the related glass and ceramics production.

By investigating manufacturing traces, the classical archaeologist Carina Weiß independently discovered that ancient glass cameos of an important private collection were made by hot-forming, using glass powder. Her investigations were supported by scientific measurements at the Mineralogical Institute of the University in Geneva. Her results belong to the foundation of the new explanation of cameo glass.

Hans Mommsen from the Institut für Strahlen- und Kernphysik of the University of Bonn, confirmed by X-ray fluorescence analysis of 14 cameo fragments of the Römisch-Germanische Museum in Cologne the result of Bimson and Freestone [J. Glass Studies 25 (1983) 55-64]. According to both investigations, the white cameo layer of a steep-walled vessel as a rule has a higher contents of lead than the dark base glass. This does not apply to flat dishes and plates. This difference can only be explained convincingly by the hot-forming of cameo glass. A lower melting point of the cameo layer, caused by the addition of lead, is desirable for steep-walled vessels during the hot-forming. It is not necessary for flat objects.

The important contribution of the classical archaeologist Erika Simon goes beyond the usual technological considerations of the book ‘Antike Glastöpferei’. However, with her iconographical analysis of the early cameo vessels, especially the Portland Vase, it is one of its highlights. Erika Simon also has a keen sense for technical details. In 1957 already, she described in her thesis about the Portland vase that the horns of the masks under the lower joints of the handles were not cut [ L1999, Abb.176, 177] . This is a very important observation. Its correctness was confirmed 10 years later by B. Ashmole, the director of the British Museum [J. Hellenic Studies 87 (1967) 1-17].

Small supplement concerning cameo glass: The above mentioned detail (no cutting around the lower attachment of the handles), firstly described by Erika Simon 1957 for the Portland Vase, applies in variations to all cameo vessels with handle(s). This detail alone would be perfectly sufficient to preclude a manufacturing of these vessels - including the Portland Vase - by cutting and grinding of a two-layered cutting blank. 

For all ‘handled’ cameo vessels,  the lower joint of the handle(s) to the vessel body was made with a lump of hot glass. This lump often was applied in a way to appear as the horns of a mask on the finished vessel - in any case without any final cutting. However, just why should a glass cutter - who assumedly finished the whole vessel by cutting the cameo decor - leave out the joint(s) of the handle(s), especially if these are extremely malformed [see the illustration Cameo glass/chariot skyphos].

It would not make sense at all to assume that the cameo decor was cut first, and the handles applied thereafter at the lower end only with a lump of hot glass - which never was corrected after cooling. No glass craftsman would doom a toilsome and time consuming cut cameo glass to almost certain destruction through reheating and additional hot work. In reality, the reheating of a cut cameo glass for the application of a handle would have been impossible in the first place because of the lower melting point of the white cameo decor.

The subsequent application of a handle is also precluded since the handles of all known ‘handled’ cameo glasses are directly connected  - not later applied (!) - to the vessel body at their upper end. This is best seen, but certainly not limited to the Auldjo jug, and has its parallels at the two-handled cups (skyphoi) of the same time. However, if a handle is a part of the body glass at its upper end, while the lower end is fused to the finished cameo decor with a lump of hot glass, this cameo decor must have been hot-formed.

The classical archaeologist and art historian Cornelius Steckner contributed his considerations about the usage of the cage cups of late antiquity. According to his conclusions, they must have been vessels for light. He experimentally checked their special qualification for this application. Naturally, such a function influenced also shape and manufacturing method of such a vessel.

The archaeologist Beat Rütti applied the new insight concerning cage cups to reconsider problems connected with the dating of the treasures from Begram. Important for him was the dating of the famous Pharos beaker, a figured cage cup with small hollow boats and the famous light-house from Alexandria on a panel attached to the beaker. Technological consideration point to a manufacture of this vessel in the same time as the other cage cups with figures or net, and this is in agreement with a new dating of the Begram treasure.

Here shall be mentioned also the work of Helmut Ricke. He was for many years the chairman of the German section of the AIHV, and he is without any doubt the best expert and promoter of studio glass in Germany. He used his experience from countless visits to workshops also in his work for the museum. The presentation of the important glass collection of the Kunstmuseum in Düsseldorf (now museum kunst palast) as well as his books and catalogues were enriched by well represented and thoroughly investigated information concerning not only the history but also the technology of glass art. It certainly was this personal conditioning which caused him from the beginning to critically observe and finally support the new perception of ancient glass technology. Perhaps, the new ideas would have faltered and become silent from the very first opposition without the encouragement from this expert.

Own glass pottery experiments

Only few improvised experiments concerning glass pottery methods were possible in different workshops. Occasionally, it was just one single trial for a certain technique. It is not claimed that these experiments can replace scientifically dependable, systematical series of experiments under close to original preconditions. These experiments also were neither suited nor aimed at the production of replicas [see supplement1 concerning the general problems of archaeological glass experiments]. Nevertheless, despite the limitations mentioned, it was possible in each case to verify or preclude the basic workability of a special manufacturing technique or working step (to be precluded is the manufacturing of reticella bowls by lamp-work).

Examples of experimental results for some illustrations see here

The experiments were made possible by the generous cooperation of the workshops and persons which are mentioned in the following:

The workshop for scientific glass blowing of Firma W. Fischer in Frankfurt and Glasbläsermeister M. Müller (reticella bowls); The Glass Studio of the Toledo Museum of Art, here the first glass pottery experiments took place with E. Marianne Stern, K. McCarthy and others (ribbed bowls); Institut für Werkstoffwissenschaften III der Universität Erlangen with M. Feldmann, K. Sandner and others (ribbed bowls and pyxides of Crete). Eischhütte und Bildwerk, Frauenau mit V. Eisch, David Hopper, B. Fleischmann and others (relief- and cameo glasses, double shell blanks). Werkstatt Molnar, Hamburg-Barsbüttel with P. and A. Molnar, H. Riecken (relief, cameo, and gold glasses, two-colored double-shell blanks, hollow vessels). Werkstatt Ittig, Wertheim with H.-J. and K.-H. Ittig, M. Schneider (overlay and relief glasses, footed bowls, two-colored double-shell blanks). The investigations and experiments concerning cameo glass were supported by the Deutsche Forschungsgemeinschaft.

Supplement 1:

Archaeological glass experiments – no simple matter

he following text (here with few additions) is composed of two short notes which were presented as part of a poster at the 15th congress of the AIHV, New York/Corning Oct. 15-20, 2001. These notes did not appear in the Annals of the congress. If you like to make citations, please mention author, congress and web site with date.  

Experiments concerning the research or a revival of ancient glass working methods are necessarily realized today at modern furnaces with modern glass material and usually with modern methods. This is perfectly o. k. if these experiments are aimed at the production of replicas for collectors. For this purpose it is only required that the replicas resemble most closely the originals. No buyer will complain about a cameo vase, which was skillfully cut from an overlay blank, if this vase does not show rotary scratches or flowing marks on its inside. A cage cup, masterly cut from a thick-walled blank, wont be worth less to the replica collector if the internal beaker does not show any bubbles which were squeezed flat. Let’s assume, a team would be concerned today with the making of replicas of ancient relief glasses, let’s assume too, they would not cut them, but they would follow the new explanation and press them. If they depend on earning their money with this activity, they could not limit themselves to use plaster molds which had to be made individually after a lost model, and which would become destroyed by one single use. They would rely instead very reasonably on multipart re-usable molds from a more stable material which would be treated by a modern mold separator to prevent the sticking of the hot glass to the mold. In all cases, the replicas could become even more beautiful, more precise and sometimes even more demanding concerning the craftsmanship required than the ancient originals - even if their manufacturing method does not at all  - or at least not in all details - equal the original manufacturing methods. Even if the glass material was molten according to analyses of the ancient originals, these replicas always will show significant details - perhaps tiny - which differentiate these replicas from the originals - and this is very much o.k.

If the goal of experiments is aimed at a scientific investigation of the evolution of ancient glass technology, it will neither be possible nor necessary to reach immediately with the first experiments the technological master-class of the time in question to reproduce the admired master-works of this time. The experience of the ancient masters in a working method which was forgotten centuries ago, as well as the workshop secrets of their time could never become revealed before at least months or even years of experiments have taken place. But, above all, experiments are of scientific value only if the preconditions are correct – and these are not fulfilled in any case today since no raw glass molten according to the ancient process is available yet.

Today, glass is molten within a few hours at high temperatures and at a controlled furnace atmosphere from chemically well defined constituents. After melting it is homogeneous and bubble-free, and it is worked immediately from the melt.

The early raw glass production was probably derived from metal melting. It was quite different from a modern glass production. During many days - maybe more than one week - natural minerals in an empirically but firmly repeated relation of volumes were molten in an earth pit, or a ventilated cave, or a special furnace at comparatively low temperatures in a more or less smoky fire. Chunks of this raw glass could later become reheated again at low temperatures together with color oxides in small crucibles. After cooling, the contents of these crucibles could be traded as round colored raw glass ingots. Working the raw glass chunks or ingots required another reheating.

We know from chemical analyses that the composition of the raw glass did basically not change during several centuries. Most surprisingly, the analyses of Roman glass resemble the analyses of a modern window glass. This is an astonishing result because modern window glass is a comparatively ‘short’ glass - meaning that the time is short during which hot window glass would be still workable before it becomes rigid. This quality is of course perfectly adapted to the production process of window glass in our days. However, the ancient glass was a ‘long glass’ - despite its similar analysis - and despite other statements in the literature because of this similarity! With a short glass it would have been impossible to trail a glass thread about 60 times around a vessel - as was done for some Mediterranean cored vessels. One could not make reticella bowls with spiral threads of up to 10 meter length. The ribs of ribbed bowls could not have been formed one after the other during one revolution of the mold with a short glass material - they could much less become corrected after that during a second revolution without reheating (Abb. 2). Extremely thin-walled blown or even thinwalled pressed (!) vessels, or playfully applied threads and handles - all this would not be possible with modern window glass, especially not at the comparatively low working temperatures of antiquity.

This discrepancy may have been caused by the visible or invisible gas content of the ancient glass. Because of the gas or bubble content, the temperature was kept high for a longer time - the longer working time. A systematical investigation would be required whether this is the correct explanation of the long workability of ancient glass. Usually the research of ancient glass technology is carried out by chemists. In this case, as in many others, glass technologists should take part.

The conclusion: Archaeological glass experiments require a reconstruction of the ancient raw glass manufacture as a sound foundation. For scientifically valid results it is not possible to limit the experiments to attractive reconstructions of beautiful ancient glasses with modern means..                                                          

R. Lierke, Aug. 18, 2003. Minor stylistic changes 30.03.07

Supplement 2:

Concerning recent replicas of reticella and ribbed bowls

At the 16th congress of the Association Internationale pour l’Histoire du Verre in September 2003 in London, very attractive new replicas of ancient glasses were presented. They appear to be a perfect illustration of the foregoing remarks.

Truly excellent reticella bowls and banded mosaic bowls were presented by the Japanese Matushima Iwao. They were made by lampwork. I have no information whether it is claimed by the artist that this technique is in accordance with the original technique. The pointed enforced flame of lampwork was not avaiable in the time when the the ancient reticella bowls were made [ L1992b]. This is supported by details of the originals (by certain trail endings, overlappings and other traces). Nevertheless, the lampworked bowls of Matushima are of remarkable resemblance to the originals, and above all, of outstanding delicacy and beauty.

Something similar could be said about the ribbed bowls of the ‘Roman Glassmakers’ Mark Taylor and David Hill. Within the last years, these two artists became well known by their remarkable experimental and commercial reproductions. In London, they presented replicas of ribbed bowls in a quality which hardly was ever seen since the days, when the originals were freshly made [www.romanglassmakers.co.uk/poster03.htm]. These bowls are truly desirable to any collector of replicas - even if their manufacturing process does not exactly confirm to the original process. Without taking away anything from the achievement of the Roman Glassmakers, here are 5 points which show that even the most beautiful replicas are not necessarily a proof for the original method.  

1. The ribs of the mass-produced Roman ribbed bowls were as a rule not painfully pinched. (suppl. 04.05.2012: a rare bowl with pinched ribs may be the mosaic bowl Nr. 969-1668, V&A Museum London). The ribbed bowls were made during more than 100 years in many variations, however almost always by the same easy and fast procedure [see techniques/ ribbed bowls]. The detail of a Roman ribbed bowl fragment [Fig. 1] shows the typical alternating steep and slanting sides of the original ribs, and the flat interstices. On the photograph, the latter are slightly slanting - just as  occasionally caused by a tool which was held in a slightly slanting position. Bowls with pinched ribs - as the replicas in London - have interstices which are bulging, not flat. This also occurs somtimes at the originals, and could easily be explained by the high surface tension of hot glass (squeezing the interstices widens the bowl, but hot glass always has the tendency to shrink back). Pinching causes both sides of the ribs to be parallel and steep. They only flatten with additional heating.

2. Reheating as a rule was not practiced for ribbed bowls in antiquity. The ancient glass was so ‘long’ that the ribs which were made during working once around the bowl, could be partly reworked during the beginning of a second revolution [Fig. 2]. As a rule, the originals show the continuing progress of the shaping of the ribs. The ribs have a tendency to become weaker (not as high and steep) towards the end of the circuit. The replicas in London had to be reheated several times during their manufacture - a rather awkward procedure.

3. As a rule, the ribs of ancient bowls are more or less curved [Fig. 3, more pronounced L1993b Fig. 17 rsp. L1999, Fig.131]. The typical shape of the ribs was unequivocally caused by working on a turning wheel. Pinched ribs are basically straight. The replicas presented in London approached the appearance of the originals through oblique positioned ribs and an occasional s-shaped rib . But, one needs to know the originals to notice the difference. By the way, the very first experiment according to [techniques/ribbed bowls] generated curved ribs [L1993b , Fig.32f].

4. The ancient ribbed bowls were not ground on their inside. This is perhaps the most decisive difference. The detail [Fig. 4, see also L1999 Fig. 22/23] shows the unpolished but glossy inside of a Roman ribbed bowl with countless pronounced scratches. It should be obvious that those scratches in a glossy surface are no grinding marks. However, the opposite is usually assumed. For that reason, the scratches were scientifically investigated. It was confirmed that the typical rotary scratches on the inside of ancient ribbed bowls (as on other ancient vessels!) are no grinding marks [see M. R. Lindig in L1999, 15-16; or here short in the summary of ‘Antike Glastöpferei’]). The Roman Glassmaker’s replicas do need extensive internal grinding to remove the traces of the sagging process, especially because of the frequent reheatings. A ribbed bowl replica with unpolished internal grinding was presented in London. To no surprise, it’s inside did show the typical diffuse roughness of a ground surface. No rotary scratches were visible, and naturally, these scratches are not to be expected to appear after the subsequent polishing.         

5. The mass-production of the ancient ribbed bowls was not a time-consuming process. The experimental shaping of ribbed bowls according to techniques/ribbed bowls, [see examples Fig. b] took less than 2-3 minutes each. But, the shaping (before grinding) of one of the replicas in London took 20 minutes. According to the information by the producers, about 90 minutes  were required thereafter for the internal grinding of each replica bowl. If for the ancient originals grinding was necessary, it was only to smooth and straighten the rim, and perhaps, to apply decorative grooves. This may have taken up to 10 minutes, but it was not at all necessary in each case.

I like to stress again that the ribbed bowl replicas of the ‘Roman Glasmakers’ are the best ribbed bowl replicas existing today. Their makers are justified to be proud. I could have chosen other examples, but all modern replicas share the same distinguishing mark: the modern homogeneous ‘heavy’ glass material - incomparable to the originals.

14. 10. 05, minor additions and slight stylistic changes 30.03.07, 04.05.12

Controversies

1. Concerning a review of ‘Antike Glastöpferei’ by B. Hoffmann

There are numerous reviews of the book ‘Antike Glastöpferei’ [L1999]. Most detailed is for instance the review of the technology expert Prof. D. Baatz in Bonner Jahrbücher 200, 2000 [2004] 647-649 (in German). A voluminous but sad example renders Birgitta Hoffmann in: Journal of Roman Archaeology 17, 2004, 621-630. I decided to comment this review here, because with numerous errors it presents a severely distorted impression of the book. The selection of wrong statements given here (extreme example the quote of Kisa, below), suggests that the book was read without attention. This may perhaps explain B. H.’s statement that the ‘Antike Glastöpferei’ is difficult to understand. Prof. E. M. Ruprechtsberger mentions the opposite: “always understandable language and fluid style” [stets verständliche Sprache und flüssige Diktion]” (Archaeologia Austriaca 84/85, 2000/2001), and E. M. Stern: “Lierke writes extremely well; her book on ancient glass pottery is as fascinating as any story of suspense” (American J. Arch.106, 2002 p. 469). 

On p. 621/622 B. H. mentions the influence of B. Schlick-Nolte and her studies of ribbed bowls on my theory of ribbed bowl manufacture - however, the distinguished Egyptologist Schlick-Nolte never was concerned with ribbed bowls at all. She was instead the co-author of my chapter on pre-Roman glass.

On p. 623  B. H. claims that I would not give any parallels for the ‘flowing lines’ in the neck of the Auldjo Jug. But actually, I furnish 3 paralleles: the Corning cameo lagynos (p. 62); a gold-glass and an agate-glass fragment (p. 64, note 36). An example in ceramics is mentioned too (p. 62, note 34).

On p. 625 B. H. claims that ‘undercut’ regions contradict my cameo theory by hot forming. However, I explain and I prove experimentally that - by using the methods of glass pottery - ‘hohl aufliegende Partien’ (hollow positioned parts) may be generated without cutting (p. 84 and fig. 217).

On p. 625 B. H. complains that I do not mention the cameo glasses with multiple layers. But I do mention them (p. 77/78 and p. 88/89). In addition, a 3-layered cameo is treated in the contribution by C. Weiß (p. 81). The making of such a cameo is illustrated in a drawing (fig. 193). The manufacturing problems of multiple layered cameo glasses are substantially reduced by moulding and the use of glass powder. 

On p. 628 B. H. claims that I missed to regard the publication of G. Scott about the Lycurgos Cup but I actually treat this paper - and almost nothing else - on 2 pages (p. 126-127) and I cite one of Scott’s illustrations (fig. 311).

Scott provided extensive evidence for the survival of cutting marks throughout the cup both inside and outside, thus - according to B. H. - contradicting my theories. But, I’m definitely aware of the cutting and polishing marks all over the Lycurgos Cup, including the fracture faces of the broken limbs and branches. The polished stumps clearly indicate that the polishing took place after this vessel was damaged - most certainly while it was mounted as chalice in the 19th century. Scott’s detailed observations support my own theories substantially, I only disagree with some of his conclusions.

On p. 621 B. H. spreads a theory about ‘the four branches of ancient glass production’: 1. free-blowing, 2. mold-blowing, 3. core-forming, 4. ‘casting’. This line-up is confused chronologically, and it is not at all  systematic (1st and 2nd are distinguished from each other like cake and Gugelhupf, and they are in addition of no concern in respect to the glass pottery. ‘Casting’ is a debated notion since ‘pouring’ was not possible in antiquity, only ‘hot forming’). Why doesn’t B. H. comment in a ‘review’ the 4 clearly distinguished manufacturing methods of glass pottery: sintering, winding, pressing, sagging?

On p. 622/23 B. H. recalls without comment the ‘evidence’ of the ‘two traditions of cameo glass manufacture’: ‘cast’ cups and blown vessels. However, this is no evidence, it is a theory which dates back to 1991 only (Soc. Ant. London Occ. Papers 13, 19-32).

With many arguments, supported by 3 of my co-authors, I show that in Early Roman times (perhaps even earlier than that, see cameo glass/ text II) there was most certainly only one method of making cameo glass: mould pressing and using glass powder for the cameo decor. Early Roman cameo glass was not cut from a double-layered blown blank as is still widely assumed.

 

On p. 625/626, B. H. presents her own theory about the making of the Auldjo Jug - with lots of courage, but without practical experience, experimental verification, or at least a close-up investigation of the original. With great self confidence, B. H. assumes that her theory will be verified by the existence of a pontil mark on the inside of the jug. With the friendly permission of V. Tattoon-Brown, I privately had investigated the Auldjo Jug twice, but, I did not remember seeing a pontil mark on its inside. With the friendly support of Paul Roberts, and in the presence of E. Marianne Stern, this investigation was repeated on 13.03.06. None of the three persons present could discover a trace of a pontil mark on the inside of the Auldjo Jug.

B. H. proposes to start with a mould-blown blue vessel which is then flashed with white glass. After the ‘creation’ of rim and handle (how?), a pontil is fixed to the inside (!) of the narrow-necked vessel, and finally, a separately made foot is applied. This procedure is partly unrealistic and it is not supported by the existing manufacturing marks. The inside of the Auldjo Jug does not show the usual negative relief from the assumed mould-blowing - not even on its thin-walled middle part (only rim and bottom of the jug are thick-walled). Flashing a mould-blown relief with a white glass layer would create bubbles between the layers - unless the work is done in vacuum. The very peculiar handle of the Auldjo Jug would require the blowing of a vessel of about 50 cm hight (!). By cutting the decor from the white layer, a continuous white ring would appear between vessel body and applied foot.

On p. 628 B. H. cites Kisa absolutely wrong: “Kisa says that the stubs did not touch the inner cup” (italics according to B. H.). She concludes from this wrong quotation that Kisa contradicts my experimental results.

But, Kisa said exactly the opposite! I quote Kisa literally about the cage cup from Hohensülzen (Kisa, Das Glas im Altertum, 1908, p.621): “Einzelne an dem Kern anhaftende Stege sind zu kurz geraten, aber nicht etwa abgebrochen, denn sie haben eine rundliche Spitze, welche offenbar das Netzwerk gar nicht berührte” [translation: “Individual struts which are attached to the core are to short, however, they are not broken off since they have a rounded tip which obviously did not touch the net at all”]. See the drawing.   

My very first cage cup rsp. double-shell vessel experiment was not a perfect success. I got a small double-shell cup (Lierke 1999, fig. 304, or here fig. j , showing this cup sawn through) with some struts not touching the outer shell. They ended instead with a rounded tip under this shell - and this is exactly what Kisa had observed (the outer shell is supposed to become the net after cutting). Should I be proud that the facts have to be turned upside down to tell that I’m wrong? 

On p. 629, in the paragraph about the digest and the diatretarius, B. H. mentions the indemnity clause for the cage cup blanks - well-known from the literature - claiming that it does not make sense with my theories. But, the opposite is true.

B. H. : “This law refers to the transfer of valuable materials from an owner to a craftsman for further work” … “but her [Lierke’s] scenario makes little sense in this context”… “an indemnity clause…would not really be relevant to the process of removing plaster after the initial moulding of a vessel, since the intrinsic value of the transferred object would have been small…” But, this is not correct. A considerable craftsmanship and amount of preparation is required for the manufacture of a double-shell cutting blank with up to 200 struts or a combination of struts with a complicated relief. This blank would enclose a perforated plaster cup which could hide cracked or imperfect struts (see the observation of Kisa above and the moulding of cage cup blanks) . At the transfer of the double-shell blank from the hot glass workshop to the glass cutter, the possibility of hidden flaws would be a perfect reason for an indemnity clause. On the other side, an indemnity clause would not be necessary for a simple thick-walled blown blank - the traditionally assumed cage cup blank. In this case, any flaws could immediately be discovered before the cutting is started, and the value of the blank would indeed not be great..

 

I’ve presented here 10 points where the reviewer failed to present or review the content of the book correctly. Unfortunately, there are about 20 additional wrong or at least questionable statements in this review. 

B. H. correctly states that within the cage cup struts a color change takes place always at some distance from the net. However, this means only that the second pressing procedure during the cage cup blank production happened while the first shell was still soft, or that both pressing procedures were combined.    

                                18.09.05 (English translation 31.10.05) , last minor additions 30.03.07.

The objection presented in this paper concerns the basic new perception of glass pottery that the typical rotary scratches of ancient glasses are not traces of grinding [ L1999, 13-16]. Pilosi/Wypyski presented instead the opinion that the rotary scratches are corroded traces of grinding and that tiny protruding trails which appear fused to the surface are in reality cords which remained standing proud on the otherwise corroded surface because of a slightly different composition.

To check whether these objections were justified, I initiated microscopical and electron microscopical investigations, and analyses at the Römisch-Germanische Zentralmuseum Mainz (Ch. Eckmann, M. Fecht and S. Künzl), and at the Fraunhofer Institut für Silicatforschung in Wertheim/Bronnbach (H. Römich and Team) respectively. My opinion was confirmed: A tiny glass trail was fused to the surface, and the typical rotary scratches of the investigated representative fragment [L1999, fig. 16-18b; see also here: Mikrophoto M. Fecht] are indeed not grinding marks [L2002b, L2004c]..

Pilosi/Wypyski show in their fig 5a (top) a scratch on a Byzantine vessel with typical horseshoe chatter marks. They compare these marks with chatter marks on the inside of a Hellenistic vessel fig. 5b (bottom), and conclude that the Hellenistic vessel was treated by cold abrasion.

However, Pilosi/Wypyski do not regard the different appearance of these chatter marks. Except for two scratches (which may have been generated somewhat later as the others), the marks in fig. 5b are no horseshoe marks any more. They are reduced to small lines perpendicular to the scratches. Exactly those reduced chatter marks were diagnosed by Dr. M. Lindig as chatter marks of ‚hot scratches’ on the inside of a ribbed bowl, see [L1999, fig. 23]. Hot scratches are generated in the solidified skin of a hot glass vessel by tiny protrusions in the surface of tools or molds. But their chatter marks are partly remolten by the internal heat of the vessel, and therefore they more or less loose their horseshoe shape. In contrast to the opinion of Pilosi/Wypyski, the inside of a Hellenistic bowl is the most likely place for the appearance of ‚hot scratches’ since they were as a rule rotary pressed. I’ve got numerous examples, including those were cold abrasion is definitely precluded for other reasons as well.

In addition, a protruding, almost circular thread structure, explained by Pilosi/Wypyski as cord which survived the corrosion of the remaining surface (Pilosi/Wypyski, fig. 6), cannot be a cord. Such cords follow the flow of the glass material - and this flow is never circular within the wall of a glass vessel. The thread on the fragment which was investigated in Mainz and Wertheim is no cord either. According to an earlier photograph, it is not standing proud because the surrounding surface is corroded, instead, it is corroded just as much or as little as the surface. The microphoto of M. Fecht, Mainz, shows the scratches passing under the thread. The analyses confirmed that it does have the same composition as the rest of the fragment.

                                                                                        18.09.05, last additions 03.04.07

D   Home Publikationen Glastöpferei Techniken Kameoglas Diatretglas Hedwigsbecher Craqueléglas Werdegang  D

E EnglishHome Publications G lassPottery T echniques Cameo Glass CageCups H edwigBeakers Craquele Vita E