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‘Antike Glastöpferei -
ein vergessenes Kapitel der Glasgeschichte’
with references to later additions and corrections by the author. For an illustrated survey of ancient manufacturing theories (mainly taken from the book) see Techniken.
For citations, you may mention this summary and website, but please, for literal quotes refer to the German original.
Ancient Glass Pottery-
A Forgotten Chapter of Glass History
by Rosemarie Lierke, with contributions by Matthias R. Lindig, Albrecht Locher, Hans Mommsen, Beat Rütti,
Birgit Schlick-Nolte, Erika Simon, Cornelius Steckner, E. Marianne Stern, Carina Weiß, and a preface by Helmut Ricke. Preface by Helmut Ricke (Vorwort, S.2)
Quotations: “Here somebody is coming who puts a major part of our knowledge in question, points to contradictions which were not discussed before, shows facts which have been overlooked - and offers
reasonable solutions for discussion... After the publication of this book, several chapters in the glass literature
have to be rewritten and some authors - the writer not excluded - have to admit that they often judged to fast, or that they simply did not look close enough.” Introduction (Einleitung, S. 3-7)
The expertise needed to write such a book was gained during 30 years of working and experimenting with glass, supported by detailed investigations of ancient glasses and their manufacturing traces. Well-known experts
supplement special topics in own contributions. The research of many years had an astonishing result, the rediscovery of a forgotten ancient glass working
method, which is a missing link and a logical step in the evolution of fire-using crafts. The forgotten method - not only, but mainly the manipulation of hot glass with molds, templates and tools on a turning wheel - is a natural
offspring of the much older art of ceramics. It is therefore called "glass pottery" by the author. The working of
hot glass on a wheel left typical traces, horizontal scratches on the inside, which traditionally are explained to be grinding or polishing marks - obviously a wrong explanation. [This result was confirmed by scientific
investigations, see
"Glass turning" by Pliny and the scratches of ancient glasses
(Gedrehtes Glas bei Plinius und die Kratzer antiker Gläser, S. 8 - 16) Pliny's description of the ancient art of glassmaking is investigated. Pliny wrote before 79 A. D. It is deduced that
his "old kind of glassmaking" describes the melting of raw glass in "continuously" (may be for weeks) heated
furnaces, followed by subsequent remelting and coloring of this raw glass before fashioning it in the glass workshops. The raw glass was a trade commodity like ingots of copper or precious stones. We have finds of
early glass ingots, a huge raw glass slab of late Roman times [may be even later] and traces of several others. Melting the raw glass in earth tanks seems to be an offspring of copper smelting. The roots of glass making
(melting the raw glass) but also of glass working (fashioning the raw glass into objects) most likely are located in
the area of today's Israel. Pliny does not explicitely mention what he considers the "new kind of glassmaking". It
is concluded here that a new way of glassmaking would be the melting of the glass constituents in the glass working place as it is practiced today. Three ways of glass working are mentioned by Pliny: blowing, turning,
and chiseling like silver. The "turning" (aliud torno teritur) so far was erroneously explained to mean the grinding
of glass on a lathe. This is hard to accomplish even today. Obviously, a turning motion was applied while the glass material was still hot. This explanation would be in agreement with the manufacturing traces, and it is
confirmed by the considerations of A. Locher.
Albrecht Locher: Naturalis Historia 36,193: "aliud torno teritur (S. 12-13) Dr. Locher (head of a Pliny translation group in the Gesellschaft Deutscher Chemiker, Tübingen/ Berlin)
investigated Pliny's glass paragraphs philologically. He concludes that his former interpretation of "aliud torno teritur" (Glastech. Ber. 52/12, 1979) was not correct. This phrase must describe a glass working
method which involved a turning motion and which is different from blowing and different from working cold glass - including grinding. The method which is described by "aliud torno teritur" therefore involved a
turning motion applied to soft or hot glass. In an addendum Dr. Locher investigates two expressions of NH 36,195.
[A. Locher interprets Pliny’s “aliud argenti modo caelatur” (chiseled like silver) as cutting rsp. engraving glass. E. M. Stern maintains that no cut/engraved glass is known from Pliny’s life time. She assumes that Pliny erroneously describes mold blown glass as “chiseled like silver” since he is not familiar with its perhaps secret manufacturing method. (personal communication).]
As mentioned, ancient glasses have typical rotary marks - so far explained to be grinding marks. They are deeply
engraved in a smooth or even shiny surface, they are not continuous, they have instead a beginning and an end, and there are usually some marks with a slightly different direction. These marks are especially ubiquituous in
glasses of Hellenistic or early Roman imperial age. Rock crystal vessels do not feature marks which fit the above description. Folds in glass vessels with the typical marks and tiny glass threads molten across the marks are
definite proof that these marks are no grinding marks. Otherwise the folds or the threads would have been removed by the grinding. The sickle shape of the accidental folds support the connection with the hot
manufacturing process. The wrong interpretation of Pliny's "aliud torno teritur" and the wrong explanation of the
rotary marks of ancient glasses as grinding marks obviously belong together. Glass was turned on a wheel while it still was hot - for instance by rotary pressing - and this process left the typical rotary marks.
Matthias R. Lindig: Investigation of the rotary marks on ancient glass (Untersuchung der umlaufenden Spuren auf antikem Glas, S. 15 - 16)
Dr. M. R. Lindig (glass technologist with the Schott Glaswerke Mainz) investigated the typical rotary marks on the inside of a ribbed bowl. He found "soft" horseshoe markings which are comparable to the
markings of a known glass production defect. This defect is caused by tiny protrusions in the mold material. The hot glass which is dropped into a mold instantly develops a solidified skin. This skin can get
scratches from irregularities in the mold surface. The scratches with their horseshoe markings are partially remolten by the hot glass. Scratches with this typical appearance are called "hot scratches". The rotary
marks of ancient glass likewise are caused by a hot manufacturing process, especially by rotary pressing. The rotary marks in reality are "hot scratches". Again, they are definitely no grinding marks.
Glass - its characteristics and its manufacturing
(Glas - seine Eigenschaften und seine Verarbeitung, S. 17 - 26)
A short introduction to the properties and reactions of glass as working material is given from an empirical point of view. Chemical formulas and analyses are omitted. Instead, the invisible strain in glass, or rather its absence
and avoidance get a special emphasis. Strain in glass may be responsible for cracks, its avoidance is important especially for the cutting of glass and for the fusing of differently colored glasses.
The erroneously diagnosed "grinding marks" of ancient glasses are partly responsible for the overestimation of
the ancient art of glass cutting. In reality, the simple cutting tools of antiquity - which are discussed in the book,
and the rarely bubble- or strainfree glass material put a limit to an extensive application of glass cutting. The problems are best illustrated by the originals.
The working of raw glass - including the addition of coloring agents during a secondary melt at rather low temperatures in small crucibles - seems to be typical of ancient glass working methods at least up to Roman
times. The raw glass was used as powder or chunks, or it was drawn into rods or molten as flat cakes. Four basic glassworking methods can be distinguished in early glass history: 1. Sintering (fusing) of powder or
chips of glass into or over a mold (including mosaics from small bits of glass); 2. trailing reheated rods or threads of molten glass around a core; 3. pressing a reheated chunk of glass into or over a mold; 4. sagging a
prefabricated flat cake of glass into or over a mold or sagging a hot glass cake over a mold by the natural flow of the viscous material (see
Early glass - an offspring of ceramics (R. Lierke and Birgit Schlick-Nolte, Das frühe Glas - ein Sproß der Keramik, S. 27 - 36)
Beginning with this chapter, the artefacts and techniques are treated mainly in chronological order. Long before
glass itself became known, the glass ingredients were worked in a ceramic-like manner. "Egyptian faience" for instance consists of the same ingredients as glass: sand, soda and lime, just with a much smaller percentage of
soda (the flux). The mixture was shaped and fired like clay. No glass recipe was required to fashion the glazed faience objects since several methods were possible to enrich the soda in the surface layer. True glass became
known - at least in Egypt - not earlier than the 16th century BC. It was added also to enrich the glazes of Egyptian faience. The first glass objects were beads and ornaments.
The working of glass was based on the experience and used the equipment of the much older faience production. The first glass vessels obviously were made by firing (sintering) glass powder. The glass vessels later
were made with tools and methods which were initially developed by the glass bead makers, a glass layer was fired over a core and the decoration trailed. From the end of the 12th century BC a shallow bowl is known with
trailed decoration. This may be the first known example which was made or at least decorated by using a turning wheel. Turner (1954) was able to prove that ancient crucibles did not withstand the high temperatures which are
necessary for casting (pouring) glass - assumed to be a neccessary precondition for molding. Especially glasses
with a relief design from this time on were described as "cut glass" instead of "pressed glass". Working raw glass,
however, does not require crucibles. A chunk of raw glass could be heated over the fire with the help of a metal rod, or it could be heated already in the mold for pressing. The temperatures necessary for pressing are much
lower than for pouring.
The climax of the glass pottery (Die Hochblüte der Glastöpferei, S. 37 - 66)
Glass probably was worked from its beginning by using the experience, the tools and workshops of the ceramic vessel production. Glasses of Hellenistic and early Roman Imperialthis time usually feature the typical rotary
scratches. The most important vessel types are discussed, see also E. M. Stern: The correlations between glass and ceramics (Wechselbeziehungen zwischen Glas und Keramik S. 58 - 61)
Many tools and vessels in a glass workshop were made from clay, very likely including the first pipes for glass blowing. Dr. Stern also investigates the influence of glass working on the ceramic vessel production.
A turning wheel was best suited for the manufacturing of bowls. Hollow vessels were firstly made by cementing two parts together, but they could finally be made in one part. Moisture in the core could even cause an inflation
(steaming) of the vessel body. They show occasionaly internal scratches or flowing marks. The invention of glass blowing put an end to the pottery of hollow glass.
A chapter by itself - the cameo glass
(Ein Kapitel für sich - das Kameoglas, S. 67 - 96) [see also The early cameo glasses (1st c. B.C and A.D) are assumed to be the "masterpieces of glass cutting of all times" -
astonishing, considering the problems of intaglio glass cutting up to late antiquity. Some cameo vessels would have required large overlay cutting blanks - a few decades after the invention of glass blowing. In the last quarter
of the 19th century, it still was a problem to get an overlay blank for the first glass copy of the Portland Vase which did not crack.
The cameo glasses have not been blown and have not been cut from overlay blanks. Sufficient evidence is revealed by: internal scratches and flowing marks, hot deformations of the cameo design, the dark vessel glass
protruding in some spots into the white cameo layer, handles molten on top of the finished cameo design, no cutting flaws but uncorrected molding flaws etc. In reality, their manufacturing technique relates to the
widespread relief ceramic production and to the manufacturing of glass cameos. For molding glass, the ceramic molds had to be replaced by plaster molds since glass does not stick to plaster. Main disadvantage of plaster
molds: they only could be used once. The plaster almost crumbles apart by itself after one heating cycle. Therefore, relief glass vessels, including cameo glass are always unique. Small glass cameos were made in plaster
molds too. If hot glass is pressed into the depressions of a mold, air could be trapped and hamper the precision. To avoid this problem, the depressions are filled with glass powder. The glass powder is sintered and the back
of the cameo pressed with a lump of hot glass on top. There are cameo plates with diameters of up to 1m! Cutting such huge plates with the primitive ancient tools would have been impossibel.
Carina Weiß: Observations at glass cameos from the Bergau collection. (Beobachtungen an Glaskameen der Sammlung Bergau, S. 80 - 82)
The Bergau collection is in the Archeological Institute of the Erlangen University. There are cameos with one, two or three glass layers, which usually are colored like their stone model. All 4 examples prove the
use of glass powder in their manufacturing process: 1. A black and white glass cameo resembling onyx, the white layer partly came off. The design is still
recognizable because the black layer underneath still shows a partly rounded relief. White glasspowder was used for the design and filled into the mold cavities. The powder shrinked during the sintering
process, the dark glass of the background therefore was pressed into the remaining space in the mold cavities. 2. A two-layered fragment of a Hellenistic glass cameo, brown on white, resembling sardonyx,
shows no even boundary between the two layers. These layers obviously have been made by subsequent filling the mold with layers of powdered glass in different colors. 3. A finely detailed black and white glass
cameo fragment resembling onyx shows a thin layer of white in enclosed areas and around the figures were only black would be expected. Obviously very fine glass powder was used, which – because of the
fine details - could not be applied to the minute details with the necessary precision. The superfluous white was not removed by cutting. 4. A two-layered glass cameo fragment, white on green, was investigated by
microprobe in the Mineralogical Institute of the University of Geneva. The white and the green glass feature different surface structures. The green glass has a homogeneous surface with slight elevations and
small pits, while the white is heavily withered and porous, indicating the use of glass powder for the white design and a molten glass chunk for the green back. There are no grinding marks at the sharp boundary
between both structures. Generally, the use of glass powder can be assumed for all cameo objects.
In agreeent with Dr. Locher, the two rather expensive glass vessels, mentioned by Pliny in NH 36,195, most
likely were cameo vessels. Pliny called them "petrotos" or "made to resemble stone" - which is exactly what
cameo glass is all about. Glass cameo vessels must be rare and expensive, no matter whether they would have been cut or made in an elaborate lost mold. The principle of making a cameo dish or bowl (see H. Mommsen: X-ray fluorescence analysis of early Roman cameo glasses (Röntgenfluoreszenzanalyse früher römischer Kameogläser, S. 85 - 87)
Prof. Dr. H. Mommsen investigated 14 ancient cameo fragments from the Römisch- Germanische Museum Köln. The X-ray fluorescence analysis induced by white synchrotron- radiation permits
quantitative results without measuring in vacuum. It is suited for measuring the element composition with radiation beam diameters of few ten micrometers - important, since in some cases the thickness of the
cameo layer measures only a few tenth of a millimeter. In 9 vessel fragments a remarkably higher PbO content was observed in the white cameo layer compared to the dark body glass. The remaining 5
specimens were fragments of flat plates or plaques. This result is in agreement with the new manufacturing theory of cameo glass. It is not necessary to have a lower melting glass powder (because of higher lead
contents) in flat or shallow molds which are easily presintered if necessary. Steep walled vessel molds are more difficult to handle with glass powder, a lower melting point of the powdered glass therefore is of
great advantage. If the cameo decor was cut, this significant difference between plaques or plates and vessels - which already was stated by earlier measurements of Bimson and Freestone - would not make sense.
While the new manufacturing theory for cameo glass plates and bowls was satisfactorily verified by experiments,
the making of hollow vessels like vases, amphoras or bottles remains theoretical. However, all of them have an undecorated neck, and some show internal flowing marks in the neck. The appearance of the typical rotary
scratches is for hollow vessels as common as for bowls. It has to be assumed that a bowl with a thick undecorated rim was made first (see Erika Simon, The Portlandvase and the Iconography of the Cameo Glass (Die Portlandvase und die Ikonographie des Kameoglases, S. 89 - 96)
In a brilliant essay - without the otherwise prevailing technological considerations of this book - Prof. Dr. Simon updates her interpretation of the Portland scenes which she firstly published in her monography of
1957. Her contribution is not summarized here, but it shall be mentioned that E. Simon was the first one to notice that at least special areas of the Vase were never touched by an
engraving or grinding wheel.
Intaglio and relief - cutting and pressing by the Romans
(Intaglio und Relief - Schleifen und Pressen bei den Römern, S. 97 - 137)
In the second half of the first century AD, the glass blowers created the attractive mold blown relief glasses, but the glass potters produced relief glasses too which are commonly mistaken to be high relief cut - and this before
the intaglio glass cutting (much easier to accomplish) really became established. Striking is the rather simple but extremely protruding relief of these glasses, and finally the missing of true cutting marks (one possible exception
is mentioned). In reality, the early "high relief cut glasses" are pressed. The simplicity of pressing those glasses
was experimentally verified. While the glass blowers were able to reuse their molds (shorter contact at lower temperatures prevented sticking; multiple parts permitted removal of the finished glass from the mold), the
pressed high relief glasses required the use of lost molds. Therefore, the pressed relief glasses are rare. Plain shapes, especially low and tall beakers pressed in re-usable molds, some with typical rings and flanges, were
decorated with enamelling or with facet cutting. Only simple cutting equipment with one or two different wheel sizes was used. Facets often remained unpolished. Other decorative pattern and figured scenes became fashion
toward the end of the first century and later. Nevertheless, the glass pottery came to a preliminary end in the first
half of the second century A. D. From this time, the blanks for facet cutting and figurative engraving were blown. A revival of the glass pottery took place in the 3rd century. It is not known what caused this revival and where
the glass pottery had survived the hiatus. High relief glasses appear again. They usually show the rotary scratches of their turning wheel manufacture and a perfectly molded relief, which again so far is erroneously considered to
be cut. Strikingly, some of these assumed "high relief cut" vessels feature miserably executed intaglio cutting in
addition to their molded relief. Facet cut beakers also reappear. They are as a rule much taller and heavier than their forerunners in the first century. Bolder and deeper facets stand for sturdier grinding equipment and for well
prepared cutting blanks. However, strain-cracks still happen. There is reason to doubt that the tall and heavy facet cut beakers were drinking vessels. Metal fittings have been found, which support the idea of a use as
lamps. Perhaps, the facet cut beakers of late antiquity can be compared with the contemporary cage cups.
Cornelius Steckner: diatreta glasses as vessels for light (Diatrete als Lichtgefäße, S. 110 - 114) Dr. C. Steckner (archaeologist and art historian with many publications) promotes the idea that the
Roman cage cups were used for lighting. Late antique glass vessels with loops for hanging leave no doubt that they were hanging lamps. Transparency, shape and decoration make these vessels attractive to look
at from below. This would likewise apply to the diatreta or cage cups which, however, do not feature the hanging loops. Two hanging lamps from Samos, dated 600 A.D., clearly are shaped like wine drinking
vessels. This makes sense, since liturgical instructions required the use of red wine as cooling liquid below the layer of lamp oil with a floating wick. The diatreta cup from Köln-Braunsfeld features a toast in Greek
letters and has no hanging loops or foot. It was assumed to be a drinking cup. Its projecting rim, however, is no invitation for drinking. 1988 a diatreta cup was published which was found with metal fittings and
three chains for hanging, thus leaving no doubt about its function as hanging lamp. The same use is indicated for the whole vessel class of cage cups. The projecting rim of the diatreta vessels this way has a
function and the cage becomes especially attractive if light is shining through. The three colors of the Köln-Braunsfeld diatretum could be explained: the letters are red, the layer of oil would respond to the
yellow collar and the cup filled with red wine under the green cage would create a color play comparable to the Lycurgus cup. This cup, picturing the metamorphosis of Ambrosia, is green but changes to red in
transmitted light. The interplay, concerning symbols and the technology of illumination on one side and shapes, colors and images on the other, connects the diatreta in technology and function with perforated
silver vessels which belong to liturgical implements.
Diatreta were explained to be drinking cups mainly for two reasons. One reason is the verse from Martial with
the first mentioning of the expression "diatretum" (end of 1st c. A.D.): "O quantum diatreta valent et quinque
comati! Tunc, cum pauper erat, non sitiebat aper!". The other reason is the occurrence of drinking toasts on many specimens. However, the diatreta or cage cups appear not earlier than the 3rd c. A.D., almost 200 years
after Martial's verse, and drinking toasts on an object not neccessarily imply that this object has to be a vessel for drinking. It is a forbidden idea to hold and handle for instance the huge Hohensülzen or the Niederemmel cup
filled with wine at their sometimes less than 2mm thick shanks and meshes. Since cage cups have no foot or stand, they could not be put down bevor they were emptied. In addition, different from engraved toasts on other
glass vessels, the drinking toasts on cage cups are always to be seen from the outside of the vessel, the inside in any case is less attractive to look at. The diatreta or cage cups therefore most certainly were lamps and not
drinking vessels. The same conclusion can be made for the tall and heavy facet cut beakers - or at least for most of them. It seems that all facet cut beakers feature one or more grooves around the rim, the possible place to fix
a hanging device. In some cases, the rim does not look appropriate for drinking at all . The question how the cage cups have been made seemed to be solved by the theory of Fremersdorf (1930 and
1956), who assumed that all cage cups were cut from thickwalled blown blanks. But, there always have been and still are serious doubts about this theory. These doubts have several reasons, just two are mentioned here in
this summary. Hardly one of the modern replicas, which have been made after Fremersdorf's theory, is as thinwalled and lightweight with slightly wavy contours as all the originals - notwithstanding the greatly improved
preconditions of our time: the use of modern tools and bubblefree glass material, or the invested time of up to several months labor (according to some artists). The originals often have internal beakers without any traces of
cutting or large flat bubbles within their rather thin walls. The bubbles are not opened by cutting as one had to expect according to the assumed manufacturing method. For a new manufacturing theory which regards the manufacturing marks of the originals, see [
It is most telling, that the typical network cage pattern basically is repeated during the whole time span when cage cups were made. Since no cage cup with this network cage pattern was cut in stone, the typical network
pattern must be caused by a treatment which is only possible with glass. The manufacturing method of diatreta glasses with figured or other scenes instead of the net basically seems not much different. A striking similarity are
the precisely flattened back sides of most figures or their limbs which can only be compared with the same kind of back sides of the cage cup meshes. This feature comes naturally from a double-shelled blank. It is certainly
most difficult if not impossible to produce rather large images or slightly curved panels (for instance the Pharos on the Begram Beaker) with a flattened back side by cutting these images or panels from a thickwalled blank.
Accidental notches around the contours of the Situla horses seem to be a proof that these horses are cut from a double-shelled blank just like the network pattern [for arguments in favor of cutting the Situla instead, see Beat Rütti: The Pharos beaker of Begram - a diatreta glass with figured scenes of late antiquity (Der Pharosbecher von Begram - ein spätantikes Figurendiatret, S. 129 - 134)
Dr. B. Rütti (Conservator of the Römermuseum Augst/CH and author of important books on Roman glass), presents a new dating of the Pharos beaker. His new evaluation is based on the new Kuschan
Chronology of Robert Göbl and a critical discussion of the dating of other glasses which are found together with the Pharos beaker. During French excavations before the 2nd world war, an assumed
former residency of the Kuschan kings at the foot of the Hindukusch was found. Two rooms were sealed. They contained treasures from the Mediterranean, from India and China. Of special interest here is the
Pharos beaker, a fragmentary diatreta glass (foot questionable restored) which shows the Pharos from Alexandria as a flat panel surrounded with several three-dimensional hollow boats. All these features are
attached to the beaker with small shanks just like the decoration on other diatreta glasses. It may be compared especially to the Budapest fish cup (4th c.) or the fragments of a diatreta glass from Athens (so
far the earliest diatreta glass, not yet securely dated to a time before 267 A.D.). On the other hand, a comparison with the Oak Leaf beaker from the end of the first century A.D. in Nijmegen is not
convincing. Here the leaves and branches are three-dimensional full round. This and other features support the conclusion that the Oak Leaf beaker is related to the high relief glasses of the first century. The Pharos
beaker instead belongs to the late antique diatreta glasses.
As already mentioned, a logical development of the Roman art of glass cutting becomes visible. While cut
grooves have been applied much earlier, the decorative glass cutting in the first century A.D. started with simple honeycomb facets, which were executed usually with just one medium sized cutting wheel. As a rule, decorative
patterns combined of facets and lines did not appear before the end of the 1st or beginning of the 2nd century A.D. They were followed by intaglio cut figured scenes. From the first half of the 2nd c. the blanks are blown. In
the 2nd half of the 3rd c. rotary pressed blanks reappear. In the 4st and perhaps still in the 5th century bolder facets, the use of more wheels of different sizes, more complex figured scenes, and even true high relief cut
cameo glasses (for instance the Hunting bowl from Stein am Rhein) show a strong progress in the cutting technique. This progress is accompagnied by a progress in the melting technology. Now true overlay with
transparent colors is possible. Blown glass obviously was made by starting with molten glass from a crucible, however, the working of prefabricated chunks of raw glass obviously was still practized by the glass potters.
Despite the progress, the technological limits of glass cutting are discernible. The late antique high relief in glass reminds more of bold wood cutting than of the delicately modelled relief of early cameo glasses. Figures on
engraved glass mostly are simplified and sketchy. Stuttered and crooked lines or other flaws and strain-cracks still occur. Polishing is rare and seldom perfect. Surprizingly, even the masterworks of Roman cut glass, the
diatreta cups, show these limits: unpolished cuts, wrong notches, and shanks sometimes almost cut through. The delicate filigree appearance of these extraordinary glasses has to be accredited for a good part to the glass
potter's preparation of the two-shelled cutting blanks. The glass cutters repertoire did not include softly rounded protruding reliefs, or cut surfaces which were perfectly
free of grinding marks. Since neither the "ceramics-related vessels" nor the cameo or high relief glasses originated
in a glass cutter's workshop, the ancient art of glass cutting never was as highly accomplished as so far assumed. The blanks of the first cut glass, the grooved and fluted bowls of late Hellenistic age for instance, and the facet
cut beakers of the first century A.D. came from a glass potter's workshop. There is reason to assume that the first glass cutters were the glass potters themselves - after all, they made the blanks. It is even possible, for
instance, that rotary grooves could be made with the prepared edge of the wheel. This and other reasons
support the idea, that the "diatretarius" may have been the glass potter. Since no diatreta glass was cut in the first century, it seems wrong to apply this name to the glass cutters.
An afterpiece - glass pottery in the Medieval age (Ein Nachspiel - Glastöpferei im Mittelalter, S. 138 - 145)
In the middle of Europe after the 5th century A.D the art of glass cutting was hardly practiced any more and the glass pottery disappeared altogether. Glass cutting survived, however, in Byzantium and was carried on in the
Islamic glass art. It is not known for sure, whether or where the glass pottery survived. There are hints that bold facet cutting again was applied to rotary pressed blanks. Related vessels with protruding discs may also have
been rotary pressed. There are Islamic glasses which show the typical rotary scratches - usually reliable signs of the glass pottery procedure.
The famous Hedwig beakers of the 12th century are supposed to be "Islamic cut glass". However, most excavated fragments appeared in southern Germany. So far neither one specimen nor fragment was excavated
or found in an Islamic country. Almost all surviving Hedwig beakers and some fragments were investigated. Peculiar manufacturing marks suggest that these beakers may have been rotary pressed. [