History of Murano glass
by Marco Piazzalunga
Glass, enamel and mosaic painting techniques are related to each other, by means of which man for more than three millennia are trying to raise the solar game of colors staring it into a material of precious appearance. It is a competition involved with nature, not so much for the forms, but just for the festival of colors.
In this race, by the force of fire, apparently deaf or opaque materials are fixed in iridescent colors, which in daylight appear constantly changing with the variation of illumination. Pure race of color, in almost all cases without organic imitation of nature, then race with abstract forms and manifestations, race finally victorious because with eternal pictorial results and yet not rigid and fixed. These products, rather than practical everyday objects also appear almost miraculous flowers, created for the enjoyment of the eyes.
From these characteristics of glass art depends the passion, evident in those who are and was devoted to outline its history, from the classic work of Anton Kisa (1908) to the many recent works, which rightly beyond the forms, they put particular attention to the colors of the vases. More than love and study, it is a joyful abandonment to their enjoyment, especially and also in examining the procedures whereby the results are reached.
Also this literary work is inflamed by this love, even better it's not the last one of its strengths. I will try to tell with passion first the outside story of Murano glass, maximum episode of this artistic technique, which connects with the fragile veils of glass blowing the ancient world to the modern. Artistic expressions come here in Murano directly from the new found techniques, so that technology and art appear more interdependent than in any other field of artistic production. The fact is cause for fruitful discussions on the relationship between technology and art, today often left aside.
I will then go on to describe, in my many articles I plan to write for this History of Murano glass, the moments and monuments of Murano glass, answering many questions that probably will overlook gradually to the reader, allowing then to introduce through a precise knowledge, a greater number of anglers in this magical realm of the art, in which it now has the feel of rare gem, now almost a flowering metaphysics, now a variant chromatic fantasy, and always the mentioned and ever-changing game of iridescent lights.
The elegance and refinement of the Venetian glass dictated the aesthetic from 1200 to 1500, the development of glass art is made after the crusades of the tenth century. To make the lagoon city famous contributed the production of vases, glasses, lightweight and elegant goblets, thin glass, transparent, pure enough to remember the rock crystal, a glass whose nature is sodium lightened with dyes such as manganese. Wonderful examples can be seen in Venice Glass Museum located in Murano, which offers a host of exhibitions and events.
Even the glass jewelry art, with special regards to glass beads, had a bloom in Venice since ancient times, and many craftsmen even today are experimenting with new techniques and color harmonies, following artistic trends ranging from floral to milky white, from chalcedony to techniques of insertion of gold leaf and aventurine. In Venice, as well as in many districts of art in North Italy you can find world-renowned artists who seek to unravel the widest possible color combinations creating fascinating examples of glass beads for Pandora or inventing elegant diffraction of colors with dichroic or transparent glass.
An interesting selection of actors in this field can be found directly from the portal of the consortium of Murano glass Promovetro.
Glass art before the advent of Murano
in Pharaonic Egypt and Alexandria
The first meeting with the glass, which in its simplest and archaic form is a mixture of a vitrifying material, the silica sand, mixed with an alkaline flux, the soda, fused together by the ardor of the fire, we do so in Egypt where in all probability it was born by accident about 4000 years before Christ, and which at first was used, with the addition of copper oxide, mainly as a glaze to cover stones in the form of beads imitating turquoise and other semi-precious stones blue and blue-green. Yet today we see with interest the work of a small circle of Italian beadmakers still loving their search for new ideas in the world of supply glass beads for Pandora oriented in the imitation of ancient Egyptian artifacts.
These beads were exported for centuries by the Egyptians in the North, East and Africa. According to some, the oldest sample of real glass does not seem to be traced back to before the Sixth Dynasty (2500 BC), and it is considered the most ancient Egyptian artifact with certain date, a "mosaic" cane laying down emblems of Amenemhat III of the Twelfth Dynasty (2000-1786 BC), preserved in the Antiquarium in Berlin.
Only around 1500 BC, as evidenced by the remains of the famous glass factory discovered at the end of the last century (1894) at Tell el-Amarna by the archaeologist Flinders Petrie, and not in the third millennium before our era, as to the beginning in 1900 it was argued by researchers as a result of a misinterpretation of known paintings of Beni-Hassan, which represent workers intent not to the blowing by a tube that goes back to the first century BC, but to the processing of metals, appear the first hollow objects made with a laborious process of wrapping glass fiber threads around a bag filled with sand attached to the end of a metallic rod which served as a handle during the entire working well and which was then wrapped in a spiral of wires constituting the neck of the object; around the latter were cast, crushing them against it by rotation, some glass fiber threads of a different color, to which was given a wavy pattern by means of metal spikes, or a trend in festoons, in feathers, these all motifs which can be regarded as the stylized version of the carvings on the stones imitated with glass background: red jasper, porphyry, lapis lazuli. Feet and handles were modeled separately, and were then attached to the piece from which it was easily then performed, after cooling, the withdrawal of the rod and removed the soul of clay.
The parts obtained with this system, which was introduced from Syria and seems widespread in Egypt by Syrian glassmakers transplanted there, they were to assume a globular or lenticular shape similar to Greek "amphorae", or vascular stretched ("alabastra"), with poor capacity and very thick and irregular walls: mostly balm containers, to hold ointments, cosmetics and fragrant essences, shaped in the manner of small vases carved in diorite, calcite or aragonite, or other semi-precious stones, and glazed dishes.
The Dynasty of which date back to these precious relics, the XVIII one (1580 to 1345 BC), may well be called the dynasty of the glass, as to it and particularly to its most famous representatives, Thutmose III (1504-1450), Amenhotpe II (1450-1425), and III (1408-1372), belong to the finest examples of this art that makes use of a material with a purity rarely exceeded in the history of glassmaking, even if largely opaque, by far preferred to transparent glass of which we have little documentation.
The background colors are usually turquoise and dark blue respectively obtained from copper and cobalt, while the decorations are made from pure red copper, and a beautiful yellow-orange. Significant are the plastic applications with glass pastes, which are in molded glass, or made up with fried compounds reduced to powder and pressed into molds of stone and then melted, or cut with the wheel of the lapidary (masks).
There are also examples of engraved glass between those found at Tell el-Amarna. Then the decline comes that lasted from the eleventh to the seventh century BC and during this time the glass makes its appearance in Greece, Cyprus and Mesopotamia (a bottom greenish glass vase engraved with cuneiform characters in the name of Sargon, king of Assyria (722-705), at the British Museum, is most probably Mesopotamian).
With Saite Dynasty XXVI (VII-VI century BC) there is no longer in ancient Egypt but in the Delta, a rebirth of the revival of ancient techniques, in archaic forms or derived from contemporary Greek pottery ("alabastra", "amphorae", "oinochoai") which are then often performed in other countries in the Middle east (especially Syria) and persisted until almost at the beginning of our era.
Perhaps the Phoenicians exercised in this period the art in their own country, making use of the same techniques, but they, like the Greeks and the Carthaginians, were more active as traders rather than as creators, and many glasses once considered Phoenicians, today with more foundation are believed to be glass instead Syrians and Egyptians, which the Phoenicians exported not only in the countries bordering the Mediterranean, but also in Central and Northern Europe.
Since the end of the sixth century onwards Alexandria became the main center of industry and from its workshops and factories go out not only many kinds of glass pastes in the form of beads and plastic reliefs, also fused mosaics, used for wall decorations and furniture and for goldsmithing, hollow glass with mosaic and "millefiori", and also glassware decorated in precious gold.
the invention of the blow pipe in the glassmaking
from its origins to the introduction of the term "murrine"
Continuing our history of Murano glass, ancient Rome, already received the power of Caesar, will spread the known glassmaking systems, as well as in Italy, where, thanks to the excellent sands of the Volturno river there are numerous workshops between Cuma and Literno, at Pozzuoli where glassmakers have their own neighborhood: the "clivus vitrearius", also in Aquileia, and in the same Urbe (in the year 14 of our era, at Porta Capena), in all the provinces of the Empire: Syria, or rather from Phoenicia where the blowing technique seems to be born, in Alexandria that even under the new rulers, will continue to be for a long time an important center of glass industry, to Gaul, Belgium, Spain, the Rhineland, where the glass in the second and third centuries of our era will rival with the Egyptian and Sidon, and even in Britain.
Although Pliny does not mention it, it is believed that the material for soliciting the melting would be used not only the "natron" of Egypt, Thrace and Macedonia, but also, and even since the time of Egyptian glass, the soda obtained from the ashes of some marine-marsh plants, including mainly "chenopodiacee" like "salsola" and "salicornia", hence the name "maritime" given to the glass manufactured with this ingredient, which are also all the glass calcium-sodium originating from the basin Mediterranean: Egyptian, Roman (Syrian and Rhine) and much later period, Venetians and Spaniards.
The frequent migrations of craftsmen from East to West favor the art and determined the formation of a style almost International of which are, however, discernible here and there different ways of manifestation. Are imitated with glass, as always attested by Pliny, various precious stones (some of these glasses camouflage are preserved in the museums, in imitation of agate and onyx, which anticipate the famous "chalcedony" of Murano in the Renaissance). Also the contemporary glass masters operating around Venice and northern Italy, often recover this ancient technique of imitation of the stones to better characterize the preciousness of some models of glass beads for Pandora, proposing a nearly infinite range of color shades inspired by nature.
It is produced red opaque glass (haematinum) and iridescent, or rather as some prefer, decorated in luster (calices allassontes versicolores) mentioned in a letter of the Emperor Hadrian to Saturnino, which test the skill of the craftsmen of the Empire in the coloring the glass with various sorts of metal oxides. Can be traced back to Pliny, according to some, even the most ancient memory of the use of glass pastes in the form of glazes, in wall mosaics (the scene of the famous theater built in 52 BC by Emilio Scauro in Rome).
In these works, as in the manufacture of beads, molten glass mosaics and chalcedony, is distinguished particularly Egypt that before and parallel to the blowing workings, refines the alloplastic techniques by pressing, through the use of convex or concave molds. Among the many imitations are those of "murrine", the mysterious and still debated precious material that came from the east, sweetly scented, color-changing, from milky white to blood red, with greasy stains that gave color of fire, with which were made vases and cups and some wanted to identify with onyx, others with the fluorspar, and others with amber, mother of pearl, Chinese porcelain or Etruscan "terracotta".
In 61 before Christ was held in the temple of Jupiter Capitoline an exhibition of authentic murrine brought by Pompeius from the East, which gave way to imitation by the Alexandrian glassmakers resident in Rome, so that "murrine" ended up being a generic commercial term that is designated luxury items made of various precious materials, both variegated semi-precious stones and imitations of the latter ones in glass.
from the "murrini" glassware
to the "lattimo" canes and "cameo" glasses
When Murano glass masters resumed in the Renaissance many ways and motifs of the Roman decoration, the historian Sabellico, in a passage of his De Venetae Urbis Situ did not hesitate, as we shall see, to define Murrini certain glassware they created probably to imitate some examples found in Alexandria in the first century BC and in the first century of our era. This is an important chapter of the history of Murano glass.
The term Murrini came not only back in fashion in the second half of the nineteenth century, when for the second time our craftsmen began to re-study the ancient techniques to exhume and start them in new splendor, but it is still very much alive on the Murano island.
The so-called roman Murrini develop the Egyptian technique of the mosaic canes, often already applied since the time of the Eighteenth Dynasty. The manufacture of these objects consists in juxtapose according to a given pattern, in a suitable refractory shaped support, segments of rods of different colors, in the longitudinal direction, or monochrome or polychrome sections formed by rods or bundles of rods previously fused together, cut in the transverse direction, or even of glassy quadrangular elements.
All these items was then placed in front of the mouth of the oven to heat until, when softened, they had welded with each other, and once cooled, the piece was patiently ground and worked on a lathe to make it perfectly polished.
Nevertheless, there are examples in which the glazed polychrome elements appear immersed in colorless glass, which would suggest that they did it with a procedure similar to that used by Murano glass masters later in the Renaissance.
Whereupon better you can see, placing behind them a rather intense light, such as the many fragments preserved in the Museum of Murano, Venice.
Even the cane of lattimo or milky glass consisting of a worm of opaque white glass twisted, enclosed in a coating of colorless transparent glass, made its first appearance in Roman glass manufacture, in the form of cords cast around the rim of the Murrini glassware or wrapped in a spiral flow around the workpiece with a procedure therefore very different from the one used later by Murano glass masters in the glasses so-called filigree and reticello.
Nor was it unknown the incision by lowering of the bottom (glass cameo) obtained by carving with the wheel of the lapidary, a layer of white glass melted over another of different color: the famous toreumata vitri mentioned by Martial of which the Barberini Vase or Portland Vase, now in the British museum, depicting the wedding of Thetis and Peleus, and the vessel of the grape harvest, now in the National Museum of Naples, are the most superb specimens. These are works of I-II century, almost certainly due to lapidary artisans not Alexandrian, but Romans, famous for their ability in engraving cameos and precious stones.
the handblown glassware and the birth of glass bottles
The first hand blown glassware into molds presumably made from clay, beared the double inscription in Greek and Latin characters, "Artas-Sidon" and later those of "Ennion", "Meges", "Neikaios", etc. probable trademarks of Syriac workshops, rather than signatures of artisans, they was in simple shapes, prismatic or cylindrical, with or without handles, smooth or with embossed vegetable (similar to contemporary clay products of Samos), masks, toilet items, liturgical Hebrew furniture, so as to suggest, for these latter glasses, a Palestinian source. It is mostly containers for ointments, perfumes, essences.
But from the first to the fourth century of our era, the most important and original industrial product of the new technique is undoubtedly the bottle: for oil, for medicines, but mainly for wine, molded into rational shapes, practical, suitable for storage, packaging and transport.
The bottles are of two types: the one, cylindrical, with polygonal cross-section, rectangular or square, with a short neck and mouth widely lipped, all rather low in height with a typical wide handle, flat, in streaks, attached at right angles from only one side; the other, cylindrical, slender, with a dual band rings on top and bottom, and one or two handles folded as in previous, but more narrow. They were probably straw as our modern flasks.
The merit of the Romans who had no particular inventive genius in the glassmaking (in the kilns of Campania the formators performed even to perfection, copies of Syriac models), but loved the gain and luxury (hence their passion for the murrine and the "diatreta" which we will discuss in a later article, and also for glass jewelry that will later be picked up by excellent European beadmakers who reinvented some inspiration from the ancient Roman colors in the famous glass beads for Pandora especially originating from Denmark and Italy), was to see in this industry "in series" of bottles, made possible by blowing into molds, a new source of wealth and know how to organize and exploit with skillness and resourcefulness of the pioneers in large part of their Empire to the famous triangle Rhone-Rhine-Seine where in the second century the viticulture was introduced.
No coincidence that the name of one of the greatest dynasties of glassmakers of this period, that of the Syriac Frontino, comes from Picardy, and that of another glazier, Julius Alexander a citizen of Carthage, that is descendants of the Syro-Phoenician, from Lyon.
With its bottles Rome opens the door of "Industrial Design" and of the production of useful forms for the needs of everyday life. After the Middle Ages also Venice in resuming the glass activity, will set up it, as we shall see, with perfect historical consistency on purely functional basis.
With the introduction of freehand blowing, and the thinning of the thickness, the number of forms multiply, simple at first (first and second century of our era), then a lot more moved, lively and imaginative, some derived from the vessels in hard stones, others from the Greek ceramics and more from silverware, as they appear from the famous finds of Boscoreale, Hildesheim and Alesia
Cinerary urns, bottles with handles in the shape of a dolphin, similar to "aryballoi" which were worn keeping them tied to the wrist, containing oils for anointing after swimming, bowls, cups and winged goblets ("pterota"), jugs, flasks, cups, some similar to the "cothones" used by soldiers and sailors, bottles with handles attached to a circle with the shape of the Greeks "diota", containers of any kind with handles of different color.
The transparent glass is decolorised to look like real crystal, and similarly to the latter appears in the homes of the wealthy, where, as Pliny tells, supersedes even precious metals.
In the second century of our era glass also inspired to a Greek poet, Mesomede already freedman of the Emperor Hadrian, some verses in which he describes the process of fusion of quartz pebbles or maybe even rock crystal pebbles, used as we have seen in a previous article, to obtain a white and transparent glass. The decoration is by winding wires in crossed lozenges, or in diamond shape, often shot around the neck, by stained glass, in drops, spots, ribs and depressions or reliefs obtained with pliers, to grinding, to engravings by wheel and sometimes in pointed diamond shapes, alone or associated with mythological scenes and in later centuries, hunting, chariot races, gladiator fights, and even the Old and New Testament scenes.
The decoration is made with motifs painted by enamel or more often cold-finished, gold-leaf engraved with ivory tip and inserted between two layers of glass welded to fire together (this technique occurs in many so-called "glass of martyrs" or "orbicular", which are funds of shallow bowls, found embedded in the concrete of niches of catacombs, with scenes taken from Jewish and early Christian symbolism, or in the production of round beads that still are made by glass jewelers in Murano to give the glass beads for Pandora superior brightness thanks to the outer layer of crystal covering the gold leaf).
But the summit of the decorative ability was reached in those little loop-shaped cups, sometimes in forms of buckets ("situlae") on which with a most patient work, the grounds were obtained by digging all around the surface and leaving only the thin struts that held the decoration adheres to the glass bottom, for which the vessel was formed by two layers, of which the outer perforated as a network. Beautiful the greenish sample of II-IV century with a hunting scene, in the Treasury of San Marco in Venice, where he also preserves a valuable situla violet in color, probably a Egyptian manufacturing from the same era, engraved with a Dionysiac scene.
Winckelmann, with a strict interpretation of a term half Greek and half Latin used by Martial and by Digesto, called them "diatreta", but with more ground before him, Celio Rovigo and Salmasio argued that "diatreta" was not a voice specific for drilled glass, but generic with which it is formerly designated all sorts of cut glass and to substantiate that claim there is the name of "diatretarii" given to a corporation of craftsmen of the glass, as opposed to the other called "vitreari", and the large number of glass objects carved and turned by the wheel left to us from the Roman world.
So while the "vitreari" manufactured and formed the blown glass, the "diatretarii" worked it in various ways by carving, decorating it with pods, ovals, circles, facets and all those motifs derived from the art of lapidary for mimic the effect of precious stones, especially of rock crystal, which are still applied today almost without substantial variations on that heavier type of glass that is closest to the real crystal which is also called by this name.
As documented by Martial, the "diatretarii" of Alexandria, who lived on the Tiber, had established all their workshops at the Circus Flaminius, but the objects made in the Urbe, in laboratories where the work was limited to pure carving, were, according to the poet, very coarser than those that were produced in the workshops of Alexandria, because here the carver worked side by side with the formator and the work that came out of their hands so acquired, right from birth, a perfect harmony between form and decoration. The "vitreari" instead had their furnaces, at the time of Alexander Severus (222-235), on Monte Celio.
and the barbaric glass
The late imperial glass items reveal more and more freedom and bizarre shapes, but sometimes beautiful, especially in non-italic regions, where many Syrians are transplanted, driven by greed for profit, typical of their own race, and impatience of a fixed abode, characteristic of glassmakers in all times (already in a decree of Constantine in 337 AD, many artisans of the glass, "vitrearii" and "diatretarii", are described as "per singulas civitates morantes", i.e. without a stable residence).
There, freed from any Hellenistic suggestion, give free rein to their true nature as blowers and formators, but not without being influenced by the imagination of the people, the Celts and Germans, among which they live. From this meeting of the Eastern genius with the Nordic genius, a "baroque" glassmaking comes denouncing the primacy of irrational values on the functional ones.
Later the forms become increasingly indeterminate and gratuitous, and the material of the glass becomes less pure, full of "pulighe" (air bubbles that are formed in the glass during melting). It is the decay of the art, of which would be seen however, from the fifth century to the eighth, the period known as Merovingian or Frankish of "teutonic" glassware, a new bloom.
Teutonic glass, manufactured with a material far from pure, full of streaks and "pulighe", are characteristic for the lack of foot (the bottom); it can probably be explained by the fact that in those days they drank standing up or lying down and the cup or the goblet, when it was empty immediately was withdrawn by the servant.
Some of them exhibit striped decorations sometimes worked with tongs, so as to form a kind of network; others have wires of different colors, knotted or comb-shaped, like the archaic Egyptians glassware and certain primitive Islamic glasses.
Also the Murano glassware known as with "feathers" or "festoons" at the end of the sixteenth century and the seventeenth century are variants more or less conscious of that family, and as we see, it got lucky in times and in countries very distant from each other.
Even today we can see in the specific work of a small part of artisans working in the Italian region of Veneto, experts in lampworking of glass rods overlapped each other and interlaced with thin gold threads, attempting to play in the category of glass beads for Pandora, the best examples of the ancient tradition of Murano "feathers" glass.
As with other families and other arts, this identity of decoration can be explained in part as a result of handing down and spread outside the original scope of certain work processes, but also the effect of the natural progression of technology in an autonomous form, independent from a pre-established tradition or from contact with other people: this is the well-known phenomenon in the applied arts, of "spontaneous polygenesis", so that the identity or similarity of the technical prerequisites, also determines the identity or similarity of the decorations in ethnic groups and in historical periods which are not linked together by any cultural setting.
A third group of "Teutonic" glasses finally, known in Germany under the name of "Russelbecher", present on the outside some empty plastic appendages, in the form of decumbent elephant trumpets, which seem to result from an oldest type of glazing where some drops of colored glass poured over the glass bottom, are "pulled" out, naturally full, so as to form hooked spikes.
Both one and the other have previous records in some late Roman glass externally decorated with shells, originating in the Rhineland and the Moselle Valley, where the introduction of viticulture had promoted the establishment of numerous glassworks.
Cologne was at this time the most important center of glassmaking. The Teutonic glass originated the typical forms of German Gothic goblets, including mainly the "Romer" which for a long time was the classic glass for the wine of the Rhine, cylindrical or conical, decorated at the base with drops, at first small, then in the middle of the fifteenth century larger and often pulled out as a tip.
and the literature of Medieval glass
Continuing deep into the vicissitudes of our history of Murano glass, as for the Byzantine glassware, once so celebrated, criticism has narrowed considerably its field today, limiting it to certain works almost exclusively decorated with enamel or engraved reliefs, and to the production of enamel mosaic, insomuch that many of the works assigned to it seem to be attributed to Eastern workshops: Egyptian, Mesopotamian, Syrian and even Persians.
In Constantinople, whose function in the art of glass was mainly that of the depository and intermediary between East and West, of the technical and artistic heritage developed over centuries of experience in the countries placed between the Mediterranean and the Persian Gulf, it certainly should be attributed, in addition to some pieces (bottles and glass cases) faceted in yellowish glass, bearing circles engraved in relief, even the "patera" made from dark violet glass, belonging to the Treasury of San Marco in Venice.
This was decorated in enamel with roses and Kufic inscriptions (perhaps added later) and figures enclosed in medallions, in late imperial style, very similar to the decorations of an ivory casket of the century VIII-X which is kept in the Victoria and Albert Museum in London. Its assignment to the tenth century Byzantine art is validated by the kind of gilding and glazing that corresponds to that described by Theophilus, who, in the treatise which we will discuss shortly, refers precisely to cups purple or blue-sapphire, made from Greeks with that procedure.
In this era instead, relatively large is the body of glass literature. Regardless of the "Mappae Clavicula" of the sixth century where it mentions only briefly the baking method for glass, for more giving a wrong recipe and prescription, it must be remembered a chapter of "Etimologie" by Isidoro (first half of the seventh century) that is linked to the Plinian didactics, and another of the "De Universo" by Rabano Mauro (844) which follows almost to the letter the previous one. In an illuminated manuscript by Rabano Mauro of the year 1023, kept in the Abbey of Montecassino, is the oldest medieval representation of a glass furnace, with the annealing kiln placed above the melting chamber, in front of which a sitting worker is blowing the glass.
Confused and obscure is the cookbook "Compositiones ad tingenda musiva" ascribed by Muratori to before the year 900, of which some chapters refer to the way the glazes of mosaic are coloured and to the fusion of glass. Packed with recipes more or less fantastic evidently derived from the ancient and medieval magical practices, is the "De Coloribus et Artibus Romanorum" by the so-called Heraclius (late tenth century). Rather less arbitrary is the namesake treaty of XII-XIII century, known under the name Pseudo-Heraclius, joined to the first, and almost always with a wonderful technical precision, especially in certain proceedings, and written with the heat of a passionate true artist; it is the famous "Diversarum Artium Schedula" by the monk Theophilus, once identified with the German benedictine goldsmith Ruggero (Rogkerus) lived in the cloister of Helmershausen in Vesfalia around 1100 year.
The most recent and documented criticism, however, considers being him a Byzantine monk expert in many arts and especially in goldsmith's and glass art, named Theophilus, who, after having traveled throughout Europe, should be established in the middle of the tenth century in the benedictine cloister of St. Pantaleon in Cologne, where he assumed the name of Ruggero.
Book II of this valuable treatise which appears in fact as a manifestation of the typical Ottonian culture is entirely dedicated to the art of glass. It describes the construction of the furnaces, the preparation of the ash and the composition of mixtures (in it he speaks about the glass made from the ashes, potassic, from beech wood, i.e. the forest glass, then called, in contrast to the sea glass "waldglas" in the German-Bohemian countries, and "verre de fougere", in the French ones, because the ashes used were also made from ferns.
Both the Teutonic glassware and the German of the Gothic period, are made with this material, yellowish, greenish or brownish. The ashes of terrestrial plants represented by the fourteenth century onwards to the Germanic countries, a very important commodity, which in the proceedings of the Hansa received the name of "potasche," which comes from its usual type of packaging made of earthenware pots called "pot" or "poit" and from "asche" which means ashes, whence the name of "potash" given later for antonomasia to the main element that distinguishes these alkalis. These ashes probably began to be manufactured in northern, central and western Europe, when, after the fall of the Roman Empire and the Barbarian Invasions were to run low the sodium ashes imported from the Mediterranean.
The Book II also speaks of "fistula" or blow pipe, of pliers, of the "trulla" or iron bucket for introducing the mixture into the oven where it is made the frit and then where the frit is passed into crucibles where the white glass is baked, and of the other tools made from iron and wood used for the glass processing (roughly equal to those used still today in workshops of Murano for example to maintain the perfect roundness of glass beads for Pandora during the rotational movement of the copper rod).
The Book also speaks of the blowing of vases, of silvering and gilding by leaf and with gold powder, and of the decoration by means of glazes, enamels in the manufacture of gold and of the glass sheets, of the composition, decoration, annealing and welding of windows, according to a widely adopted and then perfected technique by the German and especially French artists for the execution of their beautiful stained glass windows. This literature can be explained in part by the very intense activity that was carried out in the Middle Ages by alchemists in search of ways to the transmutation of the raw material and of the artificial composition of gold, as well as for the imitation of precious stones with glass.
in Egypt, Persia, Iraq, Syria
Throughout the Middle Ages, many colored glass of Roman or Byzantine or Islamic origin, were considered by public opinion precious stones and stored as such.
So it was considered the hemispherical blue Roman cup, known as "owned by the Queen Teodolinda", in the Treasury of the cathedral of Monza in Italy, which for a long time was thought to be cut by a colossal sapphire, as well as the green glass plate in the Abbey of Reichenau on Lake of Constance, called "the emerald of Charlemagne", because according to tradition, it was given to the sovereign by the Byzantine Empress Irene, and, most famous of all, the hexagonal green emerald cup with internal recess decorations, called the "Holy Basin" taken by the Genoese in 1101 during the sack of Cesarea and still preserved in the Treasury of San Lorenzo in Genoa.
This cup was believed in the past made from pure emerald and was in turn identified with the Holy Grail, or a gift of Solomon King to the Queen of Sheba, or the cup of which, after the torture, was placed the head of St. John the Baptist. Instead, it is probably a medieval Egyptian work, as no doubt is the plate of green emerald mentioned above. The emerald green glass that was made in Alexandria and Fostat (old Cairo) was well-known in the Middle Ages.
We will find in the following centuries among the Murano glassmakers, the same passion for the counterfeiting of gems that we have seen in the Roman and Islamic world. The vibrant research of complex mixtures of colors to get the tonalities and shades very similar to those of the gems, especially in ruby red, emerald green and in the blue sapphire passionates since the nineties, constantly and proudly, the refinement of the best beadmakers in their realization of glass beads for Pandora, which recently have been able to even inlcude semi-precious stones like cubic zirconia into the molten glass.
But in these centuries the art of glassmaking had a new miraculous rebirth in the East Islamic, the influence of which was heard first in the Byzantine Empire and then in Venice.
To this revival that lasted from the eighth to the fourteenth century competed all major Muslim countries: Egypt, Iraq, Persia and Syria, with stylistic characteristics, at least until the year one thousand, almost identical, given the substantial artistic and cultural unity form which arose with Islam in its early centuries of life, as could you prove the impressive series of discoveries made in 1912-1914 by a German archaeological expedition in the area of Samarra (Iraq), the famous city on the Tigris built in 840 by the Caliph Billah Motasemm, which was the residence of the Abbasids Caliphs until 970.
The Islamic glass from this period include a wide variety of types and techniques: glass mosaic similar to Alexandrian "Murrini", but different from those for a typical dull yellow color, with motifs of eyes formed by dotted circles, probably carried by Egyptian artisans moved to the capital of Mesopotamia and used as wall decorations.
Small cups and bowls in transparent yellow glass, or dark green and amethyst, also of Egyptian production of the VIII-X centuries, mold decorated with isolated or grouped dots in clusters, and sometimes stylized animals, enclosed in medallions, worked with the pliers (these glasses remind to small medallions in molded glass, used by late Roman times onwards as measures of weight or capacity).
Large bowls and cups, and more rarely mugs and jugs in dark green or amber, with Kufic inscriptions or decorations, even with pliers, in linear shapes, geometric (knots and rosettes), and sometimes zoomorphic, probably made in Egypt between the tenth and the eleventh century; even small vials and perfume bottles, in blue or green glass, often with the neck almost cylindrical, sometimes decorated to the wheel, of Egyptian origin from the centuries IX and X.
Beautifully carved bowls and plates through a blue or green surface layer, with drawings of animals and arabesques, in patterns evidently derived from similar contemporary works in Islamic rock crystal, which suggests that these objects, all assigned to the ninth and tenth centuries, have been produced by craftsmen close to those of Iraq and Egypt which in medieval times had a reputation for very talented engravers of precious stones.
Some of these have the particularity to present the detected decorations, obtained by lowering the bottom, such as cameos. The resultant effect is the most dazzling. Later a subspecies of this type to which it belongs among others, a beautiful bulb decorated with rams, kept in the Treasury of San Marco, consists of a series of glasses likely coming from Egypt in the form of calyx, decorated mostly with animals (lions, eagles, griffins) engraved in bas-relief, which in medieval Europe were used as reliquaries and are currently stored in the Treasures of the cathedrals of some cities in Germany and Poland (the so-called glassware of St. Hedwig).
Is highly controversial the source of some glass items of the treasures in the cathedral of Halberstadt in Saxony and in the Basilica of San Marco in Venice, in the form of plates or scales of circular pans, mounted in the guise of hanging lamps, decorated with concentric circles in relief or circular concave and shallow facets. Some are reproductions in glass of silver lamps described by Paul Silenziario, originally existing in the Hagia Sophia in Constantinople and so the Byzantine manufacturing; according to others they should be attributed to Persian art of the Sassanid period.
Always in the Treasury of San Marco also are included two cups, respectively in turquoise and emerald green glass, with carved reliefs of crudely stylized hares, the second of which recalls the vials of perfume and the Holy Basin of which has been discussed above, and would therefore be Egyptian, while the former, although bears engraved the words "Khorasan", it is not necessarily have to be Persian, partly because we know that it was offered as a gift to the Signoria from Agi Mohammed, legate of the Shah of Persia Uzunhassan in 1472, as authentic turquoise stone of the region, so the inscription might have had fraudulent intent.
Poor implementation was rather in the Islamic world the engraving by diamond tip, at least judging from the few pieces processed in this way and found in Samarra and Egypt.