The Beginnings of Glass

by Harry McGee © 2007


For some time I have felt it would be interesting to explore the basics of glass as a material. What is it? How did it originate? Where did its manufacture begin? What is its ancient history? And, very broad brush, how did its development progress? The following is a brief presentation covering what I’ve learned. It was presented as a slide lecture at an 11 March 2007 meeting of Glasfax in London. And since it overlaps the history of roses to some extent, it is reproduced on this website as well.

NATURAL GLASS

Glass is as old as the hills – or more accurately – it’s as old as the processes of creation. The forces that shaped the earth produced glass as a by-product. It’s a natural substance.
There are at least three ways glass forms in nature. (i) Most of what occurs in nature comes from volcanic activity. When silica is present in the semi-liquid magma that underlies the earth’s crust, you have the intense heat and the ingredients needed to make glass. And when it erupts as lava, you can find large seams of glass as it cools. We call it obsidian. Here a piece that David Dillon of the Earth Sciences department of the University of Western Ontario lent me for the lecture. It’s a specimen coming from the Rocky Mountains around Wyoming. The Roman geographer, Obsius, is the earliest known discoverer of the dark glassy rock, and Pliny duly recorded his finding. Hence this Roman’s name became attached to the rock.

  

Obsidian - a form of natural glass 


(ii) The most common method nature uses to produce glass, or obsidian, is in the intense heat of a lightning strike. When a bolt of lightning strikes a sandy beach or sand dunes anywhere, in a split second there will be beads or needles of glass formed from the silica-rich hit. Such pieces are invariably small compared with the veins of glass rock coming from volcanos. And they are usually black.

(iii) The third way nature uses its forces to create glass is extremely rare. Scientists have never been able to explain the origin of the glass balls that are found on the desert floor in south-west Egypt until recently. But it has been shown by the presence of osmium and iridium in the analysis of these spheres that they have an extraterrestrial agent in their formation. These two elements, atomic numbers 76 and 77, are transition metals of the platinum group. They are both hard; they are bluish-white and white respectively; and they look a lot like platinum. Osmium is the heaviest known metal. These two calling cards are so rare that their presence indicates they came from space. In what has been reconstructed as a blinding cosmic event, a comet or meteor came sliding into earth at a low angle over the sandy desert floor at a terrible temperature. When the cataclysm was over, there were left in its wake many thousands of glass spheres the size of bowling balls or paperweights. They are called desert glass. And unlike black obsidian, they are a light greenish colour. Similar glass bodies have been found in other parts of the world, notably Australia. Assumed to have been caused by meteorites, they are known as tektites, a word coming from the Greek for molten.

In these ways, glass preceded human history. It is far older than the animal kingdom. Only in the most recent blink of time have we begun to make it ourselves. Who would have ever guessed one might be able to see through a mixture of sand and ashes – but that is essentially what glass is. What have we learned about our earliest efforts to produce it?

ANCIENT HISTORIC GLASS

I have always admired King Sargon II of Assyria who was a powerful war lord humbling the Middle East between 721 and 705 BC. Ancient history reveals he captured all that stood in his way. His conquests are not the reason I took a liking to the strongman, but because of the what he chose to bring home with him as the spoils of victory. He showed he had a civilized side. He came home with many valuable things – including roses! He admired them! I think it becomes a man of great strength and fearlessness to have a tender regard for roses. I have spent years telling people in Québec and Ontario about the damask roses that King Sargon brought home to Damascus. Roses didn’t spread by blowing in the wind, or by attaching to animals, or floating down the river. It was people that took them from place to place – people like King Sargon. He too helped the migration of roses. Eventually they reached Alexandria, then Rome, and on to Provins in what is now France. The Moors of northern Africa took them with them when they captured Spain. The Spanish brought them to Mexico for their religious services. And that’s how the ‘Rose of Castile’ got to Rosebank. So I have been on regular speaking terms with King Sargon for many years.

  

Rose of Castile, damask rose at Rosebank, foreground, 2000
Imagine how impressed I was to stumble over this old acquaintance while I was investigating early glass. In the British Museum, there is an alabastron engraved with the name of Sargon II. Someone found it in Nimrud, Assyria, back in 1850. It is a little over three inches high. It has the shape of a small jug or vase with two lugs in place of handles. And the amazing thing is it was ground from a raw block of clear green glass – probably using a flint scraper. Between the lugs there is a cuneiform engraving: “Palace of Sargon, King of Assyria”. He probably had a whole dinner setting for 20. Maybe they contained rose water for the diners to freshen up. Or perhaps some desirable scented oil or perfume. Maybe they even held some early form of strong drink.
Well now, we know that Sargon lived in a palace. He admired objects made of glass. He loved roses – so he had an enclosed garden to protect them – no doubt formal with a reflecting pool which was de rigueur in such hot climates. He was a pretty affable fellow, don’t you think, when he wasn’t dispatching enemies.
The glass that Sargon II enjoyed was probably uncommon, but not new. We now know that glass making went way back before the first Sargon – the semi-legendary founder of the kingdom of Akkad in Mesopotamia – about 2300 BC. Excavations have shown that the earliest manufacture of glass points to western Asia about 3000 BC – five thousand years ago! Fragments have been turned up in Mesopotamia. This supersedes the evidence it started in Egypt’s Nile delta.

 

King Sargon's alabastron, c. 715 B.C. credit (1) p.20

Blue glass pendant, Western Asia, c. 715 B.C. credit (3) p. 20

 But Egypt wasn’t too far behind. Between 2500 and 2000 BC, Egyptians were turning their knowledge of glazing that they applied to other materials to using the glaze as the principal material. They began to pour hot glass into stone moulds modelled on their familiar stone and ceramic shapes. This pendant is an example. 
They began to make glass beads which were as highly prized as gold and semi-precious stones. It is interesting that these Egyptian beads were objects of trade used throughout the ancient world. This fact makes us realize that when the Europeans discovered North America, the purchase of Manhattan Island for a quantity of beads was not as cheap as we suppose – at least in the eyes of the culture obtaining the beads. They had seen gold before, but they had never laid eyes on glass beads.

 

Glass beads, Egypt, c. 200 B.C. credit (1) p. 17 


About 1500 BC, table vessels made of glass suddenly began to appear in Egypt – without any apparent transition from the solid moulded work of the past. Why? The reason for the abrupt appearance is that Tuthmosis III of Egypt conquered much of the Near East at that time, and returned to Egypt with glass makers from the region of Mesopotamia. Did he lure them back to ply their skills, or did he persuade them physically? Whatever, glass-making shops sprung up along the Nile. Most of the wares produced were small, 4 to 8 inches high, and held perfumes, oils and cosmetics. There was a ready market among the wealthy and the nobility. Here is a dark blue amphoriskos produced in Egypt about 1400 BC, almost 4" high. It was core-formed with applied handles. 

 

Core-formed dark blue amphoriskos, Egypt,       

c. 1400 B.C.  credit (1) p. 64

Of the same date is this Egyptian blue glass stand. It is extremely rare, being one of only a handful of glass objects surviving from about 1400 BC. Inscribed on it in hieroglyphics are a prayer and the cartouche of Amenhotep III. It may have been used as a base for a small figurine. These two pieces are in the British Museum. 

 

Blue glass stand, Egypt, c. 1400 B.C. credit (2) p. 32

In the Glass Pavilion of the Toledo Museum are more vessels from the period 1400 to 1200 BC. The first is an unguent bottle, also from Amenhotep’s reign. So is the footed jar. Both have applied handles and feet. The third item is a kohl tube. Ladies, kohl is a black powder (a sulphide of antimony or lead) used as a cosmetic for outlining eyes. A metallic applicator was stuck down in the kohl tube and then touched to the eyes for that Cleopatra look. The tallest of the three is 4 3/4" high.

 

Unguent bottles and kohl tube, Egypt, c. 1350 B.C.  credit (3) p. 19


Around 1200 BC, glass manufacture came to an abrupt halt during a time of political and economic turmoil. However it resumed again centuries later, and here are a number of glass vessels that were made in the late sixth through early third centuries BC. The oldest is on the left (late sixth) and I personally find it the most beautiful. I’m sure you are impressed with the artistry our human ancestors produced. Of the examples I have shown you, every one of them was core-formed, as were the vessels I showed you made a thousand years earlier. 

Glass vessels of the sixth through third century B.C.  credit (3) p. 23

Next is a core-formed amphoriskos from the eastern Mediterranean almost seven inches high made in the first century BC. See how the threads of white glass have been trailed around the body, then combed and marvered in.

Core-formed amphoriskos, Eastern Mediterranean, c. 100 B.C.  credit (1) p. 64

Five methods were used to make the glass vessels of this period:
(1) molten glass fashioned on a core. Around a metal rod, a core was made of iron-rich clay and animal dung; then dipped into molten glass – perhaps several times. Alternatively the hot glass was trailed around the core, and when thick enough, marvered on a flat surface. Details such as neck rims and handles were then applied. After annealing, the core was removed.
(2) sections of coloured glass rods fused to a core. This was used for making dishes and bowls. This technique resembled how you make a braided rug, starting at the core and winding the glass rod around, fusing it as it goes. 
(3) cutting from raw blocks of glass – like King Sargon’s dinner set.

(4)   casting in moulds. Ornaments and small statuettes were produced by either pressing in open moulds or casting in two-piece moulds. Here are two pieces that were cast. The first is late fourth century BC – a dish which was lathe cut and relief cut and polished.

Dish, lathe cut, probably Persia or Ionia, c. 380 B.C.  credit (3) p. 21

The second is a late third century footed bowl of the same manufacture. They had an excellent sense of proportion and balance. A joy forever.  

Footed bowl, probably Egypt, c. 230 B.C.  credit (3) p. 25

(5) cire perdue or lost wax method. The article is modeled in wax and covered with clay. Once the wax has been melted away, 
the gap is re-filled with molten glass
Glass manufacture flourished greatly when Alexander the Great founded Alexandria in 332 BC. Production was evident in both Alexandria and the Syrian coast – what was known as Phoenicia. Although the cultural life reflected that of Greece, the glass artisans were usually Egyptian. They clung to old ways like glue, and refused to learn the newly arrived technology of glass blowing. They called it profane and ungodly. In 27 BC, the Romans conquered Egypt. After that, fine Alexandrian glass products were exported to Rome and onward throughout the empire.

By the end of the first century BC, two important events had occurred which had a great impact on glass making. The first was the invention of glass blowing in Syria, possibly Sidon, which led to the inexpensive and efficient manufacture of glass objects. The second was the founding of the Roman empire, which allowed the established glass industries to export, through Rome, to all the known world. It was just a matter of time before local workshops would spring up in all those outposts. With the dawn of the Christian era, and the beginning of glass blowing, the ancient history of glass ends. Here are some examples of vessels produced in the first century AD employing the newfangled technique of glass blowing. This is a cinerary urn and burial goods all free-blown somewhere in the Roman Empire. 

Cinerary urn and burial goods, free blown, c. 300 A.D.  credit (1) p. 64
Next are two bottles probably from Italy (they look like Florence flasks). Both are early to mid first century.

Two bottles, probably Italy, c. 25 A.D.  credit (3) p. 31

Now comes an inscribed cup probably from Syria or Palestine, same date, blown into a three part mould; two vertical sections joined to a cup-shaped base section.

Inscribed cup, probably Syria or Palestine, c. 50 A.D.  credit (3) p. 36

CHEMISTRY OF GLASS

A dictionary will typically define glass as a hard, brittle, usually transparent, translucent, or shiny substance, made by fusing sand with soda and lime and sometimes other ingredients, and used most commonly in windows and bottles. Also any similar substance which has solidified from a molten state without crystallizing. Glass is apparently a solution which has solidified too rapidly to allow crystallization to take place.
The most important raw materials for the manufacture of common glass are calcium carbonate, sodium carbonate, and quartz. These must be very finely powdered and intimately mixed. When such a mixture is heated in a furnace the silica reacts with the carbonates, expelling carbon dioxide. After a few hours the contents of the crucible melt down into a clear liquid, which is purified by skimming, then cast or blown into moulds. Sometimes the sodium carbonate is replaced with sodium sulphate.


Flint glass is made from sand, potassium carbonate, and red lead. It was clear instead of greenish like the soda glass.
Plate glass is made by rolling a pasty mass of glass, afterward annealing and polishing. To make safety glass for car windows, you take two thin sheets of plate glass and cement them together with an organic plastic material. For optical glass, you stir the ingredients for a long time in the melting pot, cool it very slowly for up to 5 or 6 days.


In glass for modern optical instruments, all or part of the silica is replaced with boric oxide or phosphoric oxide; and part or all of the lime and soda replaced with the oxides of barium, zinc, magnesium or even aluminum. For camera lenses over f2.5, all of the silica is replaced with oxides of tantalum, tungsten and lanthanum. The index of refraction of this glass is extraordinarily high. Pyrex and other heat-resistant glasses are made by increasing the percentage of silica in glass to decrease the co-efficient of expansion. Such glass is difficult to melt so boric oxide is added to lower the melting point. Graniteware is an enameled sheet steel, and the enamel is closely related to heat-resistant glass using potassium-sodium borosilicates. (The inner lining of the Detroit - Windsor tunnel is such a material devised by Canadian Frank Engholm – grandfather of a Glasfax member.) If the enamel has tin dioxide or calcium fluoride added to it, it becomes opaque white and this is the so-called porcelain enamel of bathroom fixtures.

Glazes (like those on a tile) and enamels are really low-melting glasses. When a metal is to be enameled, the raw materials are intimately mixed and fused to form a glassy frit. This is finely powdered, suspended in water and flowed over the surface of the clean metal. The object is dried, then heated until the frit fuses, forming a continuous glassy ground-coat. The ancient Assyrians and Egyptians decorated palaces and temples with decorated bricks and terra cotta, employing this material on a scale that has never since been approached. Such decorative enamels are usually lead-potassium silicates.


Coloured glass usually owes its colour to metallic oxides which combine with the silica to form silicates. The colour often depends on the relative fineness of the colloidal particles of metal or metallic oxide. Cobalt oxide gives a blue colour; selenium dioxide or gold gives a ruby-red colour; cupric oxide, a blue under oxidizing conditions, or a dull red under reducing conditions; chromium trioxide, a green; silver oxide, a yellow; manganese dioxide, a violet. In milk glass or opal glass the semi-opacity is obtained by the addition of the oxides of tin and arsenic or calcium phosphate. There are other ingredients for different shades and the list is without end. There is no limit to the colours that can be produced by experimentation. Probably as important as the ingredient is the temperature and the timing. Too cool, or too hot, or too slow, can mess up what shade or tint or subtlety the artist is aiming for.
DISPERSAL OF THE ANCIENT GLASS-MAKING ART


We left glass manufacture back in the eastern Mediterranean (Syria, Palestine and Alexandria) with the commerce of the Roman Empire spreading its many products as widely as the Empire itself. Romans themselves were amazed how cheaply glass could be made by the glass blowing method, and glass vessels became very popular. During the first century, a steady stream of migrant craftsmen were leaving their homelands to settle in Italy, and, later, in other colonies of the West. Glass houses were soon established in Rome, and by the end of the first century to Gaul and Germany. Factories in the Rhineland and Cologne soon rivaled those in Sidon and Alexandria. In the second century ateliers in Gaul and Belgium and possibly England were producing glass too. Pieces were both mould-blown and free-blown for domestic wares, and they were in great numbers. 

The fall of the western Roman empire caused a dramatic decline in glass production. By AD 350, political power had transferred from Rome to Constantinople where artistic glass continued to be manufactured in modest amounts. The cradle of glass-making continued production in Tyre and Sidon, Palestine and Alexandria. During the fifth century art glass was made in Mesopotamia and Persia. Here are examples of glass produced in Jerusalem and Syria in the early 7th century. The hexagonal jar stands 3 3/8" high and it looks to me like the inkers I collect. The tall hexagonal jug stands 7 3/4" high. The first has Jewish symbols, the second Christian symbols.

     Glass produced in Jerusalem and Syria, c. 640 A.D.  credit (3) p. 53
During the course of the 7th century, all these near-eastern countries and Palestine and northern Africa were conquered by Arab armies under the influence of Islam, and in 634, Damascus was established as the new Islamic capital. By the 9th century, both Baghdad and Basra were highly acclaimed glass-making centres. Here is an Islamic-type of dropper flask made in Persia in the 10th century, 8 ½" high.

The Dark Ages in Europe came to an end with the Renaissance. In the 13th century, fine glassware emerged as one of the foremost luxury products manufactured in Venice. A Council of Ten governed the republic, and kept the glass industry under its control. It isolated glass-making on the island of Murano in the Venetian archipelago, to ensure better fire safety and to enforce government control. Murano became rich in technical knowledge, had good access to raw materials, and was strategically placed within an enormous trade network.

Dropper flask, Persia, c. 950 A.D.  credit (1) p. 160
Now Muranese were not permitted to leave, but the Genoese had assimilated Venetian technology. And France was the first country to persuade Genoese glassmakers to immigrate to its territory. With this breakthrough, the renaissance of glassmaking spread to all Europe – Bohemia, Sweden, England and Ireland. This cameo piece by Thomas Webb in England in the 1800s looks for all the world like the rose bowls my wife collects. In a few more years, the early 1900s, René Lalique in France would reveal his genius as a glass artist and usher in The Age of Glass. 

Cameo glass vase by Geo. Woodall of Thomas Webb,

  c. 1880 A.D.  credit (1) p. 160


We have seen glass produced by natural forces. We have looked into the chemistry of glass. We have traced man-made glass back to its earliest known beginnings – five millennia ago. We have peeked at some of the artistry that the ancients produced. And we have had the quickest glimpse of how medieval glass-making got out of the cage in Murano and spread to all the world.
Many sources have contributed to this lecture. I acknowledge a special debt to the following three books which were most helpful in putting this together – particularly for the drawings and the colour images illustrating its text:
(1) Ruth Hurst Vose: Glass, The Connoisseur, Chesterton House, London, 1975,
(2) Felice Mehlman: Phaidon Guide To Glass , Phaidon Press, Oxford, 1982,
(3) Stephano Carboni, Sidney Goldstein, Sandra Knudsen, Martha Drexler Lynn, Jutta-Annette Page, and Arlene Palmer: The Art Of Glass, Toledo Museum Of Art, D. Giles Limited, London, 2006.