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Notes for a History of Glass in Building (excerpts) By Lorenzo
Matteoli
From early history to the Roman Empire Glass had no place in warfare, at least as long as war was a matter of physical, hand-to-hand combat. War was better served by heavy stones, bronze spears or iron daggers, which is why history recorded stone, bronze and iron ages while glass never qualified for a specific 'age'. Glass, on the other hand, was used to craft jewels, brooches, small ampoules to contain precious perfumes, rare and magic essences, powerful balms, or deadly poisons. Gentle items, sweet womanly accoutrements and accessories of vanity, or else mean tools of secret perfidy. All of these were inconsistent with the resounding glory of the kind of events generally assumed to 'make history', such as wars, massacres, battles, conquests, dazzling victories and gruesome defeats. Thus it is difficult to know exactly where and when the melting of silica sand, mixed with the right parts of soda and lime, was mastered for the first time in order to yield a translucent paste which could be shaped into desired forms and designed objects. Pliny the Elder tells an interesting story about Phoenician merchants carrying a cargo of natural soda blocks which, for want of anything else, during an overnight stop, they employed to protect their fires from the wind and to support their pots, on an unidentified Mediterranean beach. The day after, in the ashes where the blocks had previously stood on the sand, they found a dark translucent magma glimmering in the early morning sun: the first glass ever produced. Here is the story in Pliny's own words: '.......fama est, adpulsa nave mercatorum nitri, quum sparsi per litus epulas pararent, nec essent cortinis adtollendis lapidum occasio, glebas nitri e nave subdidisse. Quibus accensis permixta arena litoris, translucentes novi liquoris fluxisse rivos, et hanc fuisse originem vitri'. Pliny's account is plausible, and, if not true, a well-deserving fiction, in line with most of his stories . Among the many weaknesses of Pliny's account the most striking is the total lack of information on why the Phoenicians were carrying Soda: a flux needed to lower the temperature at which silica sand liquifies in glass furnaces. No Phoenician merchant would carry around heavy cargoes of soda if not to sell them to somebody that needed them and, at the time, glassmakers would have been the only interested parties. Glass has been present in nature since ever as the product of high temperature processes involving silica rocks or sands: lightning accidentally striking sandy beaches or volcanic lava meeting siliceous rocks produce blobs or vitreous rocks. Meteors crossing the atmosphere can be partially vitrified when they reach the ground. The enormous pressures generated by tectonic movements also yielded high temperatures of internal masses. Natural glass can be more or less transparent or pure, and has been known to men for millennia. The temperatures of those natural accidents are in the range of the 2500-3000 °C: way beyond the temperatures men could reach with wood fired furnaces. Even when you know that silica sand treated at high temperature yields glass, the reproduction of the process is not at all easy and many other secrets have to be discovered, many techniques have to be acquired. The highest temperature you can reach burning wood is in the range of 700 °C, a consistent increment was possible when the process of transforming wood into charcoal was learned, but still the temperature of a charcoal fired furnace would not exceed the 1000 °C. Strong, forced ventilation on the burning fuel would boost up the temperatuire to 1200 °C, which still would not be sufficient to liquify siliceous sand that melts well above 2000 °C . Adding a proper alkaline flux, soda or potash, in the right proportion the melting temperature is conveniently lowered. But still you would not obtain glass but a vitreous frit. That frit has to be cooled, ground and fired again at 800-900 °C. To obtain a completely liquified mass without impurities and air bubbles, the temperature must be sustained for days and cullets of broken glass have to be added to induce complete liquidification of the frit and a reasonably pure molten glass. Mechanically induced ventilation requires the understanding of how a bellow works: the simple suction/pressure valve system may appear simple to us, but several hundreds years passed since the temperature of naturallly drafted fire was boosted with a proper blower. Many other details had to be devised, invented, designed, built, tested, improved: the furnace, its internal refractory lining, the mass of the walls and their heat resistance, the respective position of the fire and the crucible, the refractory ceramic material for the crucible, the tools to handle the crucible and the molten glass, just to list some of the most important features. Then the subtleties of the mixture of siliceous sand and fluxes, the craft needed to shape the molten glass and the techniques to avoid thermal stresses, fragility or breakage during the cooling cycle. The knowledge of the art was a family treasure: the secrets jealously transferred from one generation to the other, each one adding bits of experience and know-how. For those who did not belong to the extended family or tribe there was no way to learn the secrets of the trade. Mastery of glassmaking probably came with the combination of two crafts: the glazing of early pottery and the smelting of iron. The first implied the chemical know-how to combine silica sands, alkaline fluxes and metal oxides for the vitrification and decoration of ceramic surfaces, the second the knowledge of pyrotechnologies: how to fire a furnace with pneumatically enhanced draft to raise the temperature of the combustion and induce the chemical reaction for the refinement of mineral ore. Archaeological findings carefully dated supply enough evidence to locate the event in Mesopotamia during the third millennium B.C. There the Semitic tribes of the Amorites and Hurrians, masters of iron metallurgy, met the Sumerians potters and that was the origin of Glass. The Amorites later moved to the mediterranean coast and mixed with the Akkadians. They brought there their knowledge and the craft of Glassmaking was established as a Jewish trade. For a long time, and up to 1960, historians thought that glassmaking was originally mastered by the Egyptians: for the main reason that in the tombs of the Pharaohs many glass items were found like pots, vases, small bottles for perfumes and essences, jewelry. The "Egyptian assumption" implied a lot of mysteries and inconsistencies that were systematically waived by historians probably too fond of the Egyptian myth. The chemical composition of the Egyptian items had large percentages of potash that is not present in Egyptian natron (soda), also the cobalt found in blue glasses is not available anywhere in Egypt. Moreover other archaeological findings in Syria (Ebla), Mesopotamia (Ur), were dated with great certainty to be much older that the Egyptian items. But so strong was the academic patronage for the Egyptian assumption that any other challenging hypothesis was disregarded and dismissed. It is only in the late nineteeneighties that the origin of Glass has been correctly placed in history and in geography. The conclusive work on the subject is by Samuel Kurinsky and was published in 1991. Glassmaking was brought to Egypt by Akkadian tribes: Egyptian glass was the product of Semitic peoples migrated to the region or brought there by the Pharaohs. There is ample evidence that Egyptian glassmaking was based on glass imported from Akkadian territories. When the Jewish tribes left Egypt, glassmaking is discontinued forever in that region.
The end of "antiquity" The twelve hundred years between the final collapse of the Roman Empire and the Renaissance, are known as 'The Middle Ages', and the first five centuries have been labeled with the menacing qualifier of 'The Dark Ages'. Historians of the Renaissance branded the whole period with negative terms, mainly due to their own longing for self appreciation: they were the bearers of the new light and before them there was nothing but a world of gloom, pestilence, famine and violent, feudal oppression. On account of the biased scope of the early Renaissance researchers, for a long time little attention was given to the vast set of documents and data on the early centuries of the Christian Era. The reassessment of the values and of the cultural strength of the early Medieval centuries is an achievement of recent historical research , possibly associated with the radical evolution of cultural values that took place between 1965 and 1975. The fall of the Roman Empire, the barbarian migrations and invasions were generally reported, by institutional history text-books, in a radical, abridged way to cover, almost without any other detailed event, some five centuries from c. 500 AD to c. 1000 AD, centuries which were dismissed as the dark centuries. On account of this assumption Europe seems to have switched directly from Emperor Constantine to the splendor of the gothic cathedrals marking the dawn of Renaissance. Western and Central Europe have always had problems with the Eastern culture: the suspicion of duplicity is still rooted in the word "Byzantine", and the Eastern culture always regarded people from the West as rude and coarse red-necks. The West had a conceited, empire-centred attitude, very much resented by the culture of the Eastern Empire. Emperor Nicephorus II Phocas quite frankly expressed that feeling in the curse he uttered to Liutprand from Cremona , then Western Ambassador to Costantinople: "Vos non Romani, sed Langobardi estis!" (You are not Romans, but Longobards!") . That was the end of any negotiation for the unsuccessful mission and, probably, the beginning of a cultural split that is still felt to day. Even if some historians think that the influence of Bysantium is underestimated, for many others the suspicion still lingers. The settlement in Celtic Europe of peoples coming from the east was a slow process started some 3000 years BC and eventually stabilized c. 1500 AD. Over four millennia there was a continuous migration of tribes and peoples from the East to the West, pushed by climatic changes in the trans Ural plains and attracted by the green European valleys. The somewhat stable period of the Roman Empire was an important exception, but, even during Roman rule , the movements and settlements of Teutons, Hermaduri, Ligures, Aedui, Marcomanni, Thracians, Dacians, Senones, Alemanni, Vandals, Huns, Burgundians, Franks, Lombards, Thuringians, Visigoths, Ostrogoths, Iberians, Balts, Slavs, Saxons and Arabs, shaped future European geography. Some of these are still open problems . The Romans, however, established a well organized system of rules, laws and mandates, in their territories and managed them for some hundreds of years. Every subject was a Roman Citizen, and Latin was the unifying language, local cultures and structures, though respected, were overwhelmed, rarely absorbed and assumed. By the end of the Empire, dependence upon the center of the 'chain of command' became more and more loose: Rome demanded loyalty and collected tributes through appointed imperial officers (proconsuls), but they did not closely police the cities, nor did they militarily control the territories. The Roman Legions were a deterrent for the barbarians, but neither necessarily, nor always, an active presence in the Provinces. Roman jurisdiction was very much a matter of mutual agreement, based upon mutual advantages and benefits. After the year 313 AD the Church acquired considerable secular power. The important change in the course of history was due to Emperor Constantine the Great (b. c. 289 AD d. 337 AD) who declared official tolerance for Christians and who himself became a Christian. The official act that issued this imperial decision was one of the points in the Edict of Milan (313 AD): the treaty signed with Licinius after the final victory against Maxentius (Battle of the Milvian Bridge). The imperial tolerance, at first, and then his strong support, set the foundation for what was to be called Christendom: the Reign of Christ on Earth. The moral and religious authority was conveniently assisted by secular power: Bishops administered justice and collected tributes 'on behalf', or 'in the name of' the Emperor. The imperial beaurocracy slowly gave way to a different administrative structure. After Constantine's death, thanks to a forged testament of the Emperor, the Church of Rome claimed a right on the whole Roman Empire. Bearing all this in mind, the so called collapse of the Roman Empire appears more like a slow fading away of the central node of the system, a process that may have been barely perceived by the periphery. The peripheral system had become more important than its central node. This long event can be regarded as the final step in a process of 'decentralization': a process that is today considered vital for government and management efficacy. The cultural evaluation of the collapse of the Roman Empire given by the Renaissance, and apparently accepted by contemporary critics until the nineteen fifties, is consistent with the values which favoured strong, centrally dominated organizations up until our present times. These comments may appear beyond the scope of this work. It is, however, intriguing to remember that things did, in fact, evolve with a different pace than is usually suggested or assumed. The strong influence on historical records of an Empire-centred stance may have obscured, to our eyes, that outside Rome there was not a wild jungle, and whatever came after the collapse was not necessarily all dark. Barbarian invasions did not happen as a sudden catastrophe: sometimes they were bloody and violent raids, sometimes they were the result of peaceful migrations, at other times they were acts of war, lasting decades. Despite the term barbarians, some of the ethnic groups enjoyed, in many fields, a cultural level comparable, if not superior, to that of the Romans. Planning and leading huge migrations required leadership, organizational skill and consistent technological support. The Teutons brought new vigor and new technologies: sturdy plough-shares fit for turning heavy, unbroken soil, increased production and expanded cultivated land; some important innovation in horse harnessing allowed great improvement in the use of animal power for warfare, transportation and plowing. These barbarians also introduced the process of boiling animal and vegetable fats with a strong alkali to produce soap. Unprecedented personal hygiene and health improvements were important consequences. There may have been a stagnation of international commerce, but the basic trades managed to survive through the difficulty of land transportation and the risks associated with the long journeys (bandits, vagrants, tolls imposed by local chieftains or by feudal rulers). Regional and district trading was lively and supported by local currencies and coinage: the birth of the modern international monetary system. Roman Laws became local laws and blended with tribal codes ; justice was granted and administered by the local rulers or by representatives of the Church entitled by the 'ban . Common interest in order was a much stronger bond than raids by outlaws or bandits. Life in the 'court' was pleasant and solidarity was the mark: the dangers outside made the court a 'safe' and cherished place. The strong mark of these centuries in Europe was the slow and not always easy process of conversion to Christianity: Clovis, the legendary king of the Franks who was baptized with his entire army was an exception. Almost defeated, he prayed to the Lord of his beloved Christian wife Clotilda and the battle ended in victory. So we learn from St. Gregory of Tours' History of the Franks written in a very simple language enriched with colourful episodes that shed a very humane light on those years. The 'Dark' Ages were as dark, or as enlightened, as any other age of history. The negative qualifier has slandered a period of time that successfully managed the difficult and long transition between a central strong rule to a decentralized, regional set up, to a rule responsive to local conditions, when a multicultural and multi-ethnic Europe started to face and deal with its complex, diverse personalities. These very diversities have been, in the centuries that followed and up to our time, both the unique cultural strength and the creative political weakness of the Old Continent. To support this point I quote a few excerpts from Nora Chadwick's 'The Celts': 'Celtic culture is the fine flower of the Iron Age, the last phase of European material and intellectual development before the Mediterranean World spread northwards over the Continent and linked it to the World of today.'
'...In general, the technological level of the La Tene Celts, with very few exceptions, was equal to, and in some matters surpassed, that of the Romans. It was inevitable, however, that in any conflict between Celts and Romans, the superior powers of organization, sense of discipline and general orderliness of the Roman culture were bound to overcome the volatile and undisciplined Celts whose sense of loyalty, powerful though it might have been, was normally centered on an individual rather than on an institution or on an ideal.' .... 'The contribution made by the classical World has not been doubted since the Renaissance, and has sometimes been exaggerated. It is time that the contribution of prehistoric Europe, and more particularly that of the Celts and their forebears, was recognized adequately.'
The cultural roots of Europe, that since the Renaissance have always been thought as deeply sunk into the tradition of the Roman Empire, may appear with a different light. Some concern about the long history of the Celts could be useful to understand the many cultures that interact in present day Europe. Theophilus Presbyter Very little would be known about glass technology in the Middle Ages if it were not for the diligent work of a monk, Theophilus Presbyter, who wrote, around the year 1000, a comprehensive technological manual entitled 'Diversarum Artium Schedula'. Today only eight handwritten copies of it can be found in European Libraries. Conceptually very modern and enlightening, the book describes in practical detail, and with some fantasy, the state of the art of a set of technologies or manufacturing processes, one of which was glass manufacturing. The work was published (not complete) in Germany by G.E. Lessing (Lessius), who found a handwritten copy in the Wolfenbuttel Library, and printed by Leiste in 1781, and later in London the printer Raspe published the first 'liber'. In 1843 the complete work of Theophilus was published by the Count de l'Escalopier. From this edition the French Librairie du Dictionnaire Des Arts et Manufactures (Paris) published the second book, translated by George Bontemps. Bontemps was the French glass expert who advised the British industrialist Lucas Chance in 1830 when he started a sheet glass production in England. The translation is accompanied by a commentary based on the personal experience of Monsieur Bontemps, who cannot refrain from seeking to clarify the sometimes obscure and technically vague text of Theophilus. Bontemps generously supplements data and information drawing on his personal competence. This is an excerpt from his preface to the translation of Theophilus' work:
'...the publication of this work has been for me a most fortunate contingency; in fact all through my life not only have I always studied the art of glass making, but the history of this craft as well. I have always been a great admirer of the ancient Egyptian and Roman glass makers (whose marvelous masterpieces contemporary craftsmen would not be capable of challenging, all progress notwithstanding), of the Venetian masters and of the decorated windows of our ancient cathedrals, and I have always nurtured great curiosity for any document and information on this art. Therefore I feel the greatest gratitude for the Count de L'Escalopier who published the Latin text of the works of Theophilus Presbyter. To read the manuscript one should have studied paleography and I would never have had the time to go to the library and read 'Diversarum Artium Schedula'. Having duly paid this tribute to the merits of the Count Lord de L'Escalopier, it is also my duty to say that I deemed his translation far from satisfactory. It is a fact that the knowledge of a language is not sufficient to translate a technical work. A humanist will never be able to translate a treaty on Mathematics or on Chemistry, let alone a Technological Manual. This is why I took the responsibility to re-edit the translation of the Second Book of Theophilus' Treaty, so that contemporary glass making masters, who do not know the Latin language, or who have forgotten it, can read what in other times our colleague, and brother in craft, Theophilus had to say...' (translation by LM) Very little is known about Theophilus. Bontemps assumes that he must have been German from a jargon term that the monk was not able to translate into Latin: to indicate a grey/blue colour Theophilus uses the term 'posch' which Bontemps classifies as being'... without any doubt a German touch !' It would not be right to report the words and opinions of the translator and make no reference to the words of the author. Let us read a few lines of his original manuscript and let us think about him while he peacefully works in his clear and luminous cell in a German Abbey, in the midst of the woody hills along the Rhine, after the matins and lauds and before going to his glassmaking workshop to produce, for the Glory of the Lord, for the wealth of the Monastery, for his Brothers in Christ and for the Holy Services, beautiful and delicate chalices with marvelous colours, often obtained by sheer chance, thanks to the alchemy and secret recipes of the ancient masters. And here we are at the dawn of the second Millennium.
Prologus Liber Secundus '... Scire aliquid laus est, culpa est nil discere velle... Nec quispiam, eum, de quo Salomon ait: qui addit scientiam, addit laborem, apprehendere; quia, quantus ex eo procedat animae corporisque profectus, diligens meditator poterit advertere. Nam luce clarius constat, quia, quisquis otio studet ac levitati, fabulis quoque supervacuis operam dat, et scurrilitati, curiositati, potationi, ebrietati, rixae, pugnae, homicidio, luxuriae, furtis, sacrilegis, perjuriis et caeteris huiusmodi, quae contraria sunt oculis Dei respicientis super humilem et quietum et operantem in silentio in nomine Domini et obedientem praecepto Beati Pauli Apostoli: magis autem laboret operando manibus suis, quod bonum est, ut habeat unde tribuat necessitatem patienti.'
For those unfamiliar with Latin the short, but clear statement with which Theophilus opens his Second Book of 'technical specifications' reads somewhat like this:
Preface to the Second Book. There is great merit in knowledge, great shame in the unwillingness to learn... No doubt must we have in imitating those who, as Solomon says, increasing their knowledge make their work more useful, in as much as we will have the means to ascertain this truth, we will make our soul and our body better as well. Is it not clearer than light that he who does indulge in idleness and in futile things shall also lean on vanity, carelessness, inept curiosity, drunkenness, brawls, homicide, carnal desire, theft, sacrilege and all the other filthy enterprises that will take the eyes of our Lord away from him, who instead looks upon the humble man who in serene silence works with his hands, obeying the teaching of Apostle Paul so as to have something with which to bring help to our suffering neighbour' (translation by LM)
After this preface begins the second book of the 'schedula':
LIBER SECUNDUS Caput I De constructione furni ad operandum vitrum. Si sederit in animo ut vitrum componas, primum incide ligna faginea et exsicca ea. Deinde combure ea pariter in loco mundo et cinere diligenter colligens, cave ne quicquam terrae vel lapidis commisceas...
Second Book Chapter I If you have in mind to produce glass you have first of all to cut beech wood and dry it up. Then burn it in a clean place and collect the ashes, taking good care that no dirt or stones get mixed with them ... (translation by LM) Theophilus' handbook is quite comprehensive, Monsieur Bontemps' complaints notwithstanding, in Chapter VI the reader learns how to make sheet glass (Quomodo operentur vitreae tabulae) and in Chapter XXVII you are taught how to join small glass panes by means of carefully moulded lead and tin flexible profiles to glaze large windows (De conjungendis et solidandis fenestris) : the technology that brought glass into the history of architecture. Theophilus' book and a careful study of what is left of the great stained glass windows on the European cathedrals can help us in describing the state of the art of glass technology between the year 1100 and 1250. The reason for the scant documentation on glass technology is the strong protection of the trade on their know-how. The trade was also protected by Kings and Lords: the licence to allow a glass-maker to work on some important project abroad was often an item negotiated at the level of the King himself. Venice was not available for that practice and allowed only the exchange of goods and not of the technology or its masters. All this makes Theophilus' book even more precious: whoever he was he was very well informed at quite possibly a glass-maker himself: some of the details require first hand experience. Theophilus was also a caring teacher: he is always very keen in preventing his readers from any damage or danger like when he recommends the blower to always keep the mouth off the pipe when not blowing, to avoid inhaling hot air that would seriously burn mouth and lungs.
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