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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.
The origins of Glass and the first 3000 years
A major weakness of Pliny’s account of the origins of glass 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 (to increase the temperature of the combustion)
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.
Mastership 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: the political correctness can now accept the history of glass
as a "Jewish History".
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.
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 the author)
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 the author)
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 the author)
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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