by: Susan Hampton
Glass vase with trailing patterns
The origin of glass is not precisely known. Glass making has been around for millenia, but the art of glass blowing is a more recent invention which originated around 50 B.C.. There are many different methods of shaping glass, as well as different ways to color it. Thousands of examples of ancient glass have survived, and we can examine them to compare ancient techniques with modern practices. There are also a few ancient glass-blowing sites, and, while they are not well preserved, they are of some interest. Since there are no written records of the actual process of glass blowing, I will give comparative evidence from colonial Jamestown in Virginia.
In our high-tech, fast-paced world of modern conveniences we take so many things for granted. With the mass production of so many things, such as cloth, glass, and even food, we have lost touch with the actual processes necessary to make these essential items. Glass was at one point in history a very valuable commodity available only in small sizes and to the extremely wealthy. With the invention of glass blowing, glass became a material accessible to the general public.
It is amazing to think that sand, sodium carbonate, often formed by burning seaweed, and lime can be transformed into a substance with limitless possibilities. Glass is a beautiful medium which can be used to make household items such as windows and mirrors, or transformed into delicate art. There is something intriguing about the way a glob of molten glass can be transformed into magnificent objects. Each piece of glass that is found reflects "the ideas of its maker, of the techniques, practices, and styles alive at the very moment at which it was made." (Zerwick, 7) Something about glass draws me to it. Is it the duality of its nature, so hard and beautiful and yet so fragile? Thomas Buechner expressed my instinctive feelings about glass very eloquently when he said
Glass has a magic about it, that it seems to fascinate both makers and owners regardless of when or where they live. Perhaps it is because glass is molten and moving and untouchable in the very moment of its formation that the craftsman must respond with great speed and certainty. Perhaps it is its split nature- opaque or transparent, colored or clear, fragile or strong. Perhaps it is its seemingly endless potential. (Zerwick, 7)
Maybe it is fitting that we have no definitive answer as to what is the origin of glass making. It lends to the mystique that the most widely known explanation is a myth handed down to us from Pliny the Elder. In the part of Syria adjoining Judea and Phonicia the Swamp Candebia is bounded by Mount Carmel. This is believed to be the source of the river Belus, which after five miles runs into the sea near Ptolemais. (Pliny, 361) On the shores of the River Belus the sand is revealed only when the tides retreat. This sand "does not glisten until it has been tossed about by the waves and had its impurities removed by the sea." It is upon this fabled stretch of sand that glass was discovered by some traders who had come ashore to eat.
A ship belonging to traders in soda once called here, so the story goes, and they spread out along the shore to make a meal. There were no stones to support their cooking-pots, so they placed lumps of soda from their ship under them. When these became hot and fused with the sand on the beach, streams of an unknown liquid flowed, and this was the origin of glass. (Pliny, 362)
Admittedly this is a myth told by the Phoenicians, who quite often told stories to make themselves look like the source of many great inventions. Possibly they did invent the technique of glass blowing, but many older techniques, such as casting, cutting and grinding, had been around much longer.
"The earliest man-made glass had been produced more than 2,000 years before the founding of the Roman Empire. By 1500 B.C., craftsmen in Mesopotamia and Egypt were making small brightly colored vessels." (Whitehouse, 5) It seems most likely that glass making spread from western Asia and Egypt. From archaeological discoveries we have discerned that some of the earliest blown glass was found in Palestine and Syria. (Whitehouse, 5) What we have to remember is the vast range of the Roman Empire during the early years of glass blowing. Although along today's political borders, places like Eygpt and Mesopotomia seem distant from Rome; Harden shows how much of the known world Rome ruled with this sketched map. (Harden 1987, 10-11)
Glass making did not originate near the "heart" of the Roman Empire, but many advances were made in Italy when it was transported there. "In the reign of the first Roman emperor, Augustus (27 B.C.-A.D. 14), glassmakers established themselves in Rome and other parts of Italy." They were still using the older method of forming glass at this time, casting it in pre-made "blank" molds, very similar to the "terra sigillata" technique used in pottery. Many examples of this are thought to have come from Adria, near the northeastern coast of Italy. There is one cast green "boat" vessel that was found in Pompeii that is believed to come from the second quarter of the 1st century AD. (Newby, 4) This is important because it can be specifically dated to within about 100 years because Pompeii was buried in ash in 79 AD.. Unfortunately the history of many surviving glass artifacts has been lost because they were kept in private collections and then later given to museums. As is the case with all archaeological evidence, if you take the artifact out of its original context, much of the meaning is lost. This has happened with hundreds of glass pieces, so although approximate times and places of origin can be given to the artifacts on the basis of what is known about the period and style of the piece, we are often left with unanswerable questions.
In ancient times molten glass was kept in a liquid state using a wood-burning furnace. It takes a lot of wood to heat a furnace over 1000 degrees. We don't have any specific details from Roman times, but Pam Rossmen from the Jamestown glasshouse gave a comparison from 1608 A.D. It would take enough wood to build a two story house to heat the furnace for just one run of glass. Imagining how much glass was being made through out the empire and it is easy to see how the natural wood supplies would become exhausted quickly. This forced the glassmakers to move to other districts once they had exhausted the wood in the surrounding forest. Glass making was not an environmentally friendly process.
"Perhaps these conditions affected the character of the workmen themselves, for they were apparently restless in spirit, and seemed to prefer the itinerant life to a settled existence in one place," (Robertson, 20) There is yet another explanation as to why it is so difficult to date glass objects to certain places and times; a far more romantic notion which I find much more appealing. Glassmakers were an independent and creative bunch, with a "touchy pride" that made them difficult at times for outsiders to deal with. I love the image of carefree glass-blowers roaming the continent with no one to answer to but themselves. As the artists moved around, they took their techniques and styles with them. "Athough some areas had special styles and characteristic forms, glassmakers traveled extensively and there was little delay between the introduction of a new idea and its application hundreds of miles away." (Edwards, 5-6) One specific style of making glass was never confined to a single region because the workers were constantly changing, or learning new techniques from newly arrived artisans. Although the glass factories of today cannot be moved around at the whim of a master, the workmen are free to move and change masters whenever they wish. This they do in the same unsettled manner of their ancient predecessors. (Robertson, 20)
There are not many sites of ancient glass blowing houses, but there have been partial remains found in Eigelstein, near Cologne, and in Phiadius in Greece dating from the 5th century B.C.. Pieces of glass from half of a mold, partial remains of a glass furnace and a crucible in which the glass was heated to a molten state, are all artifacts found at these sites. (Price, 118) Along with sites we have a multitude of glass objects, and although many cannot be placed, we have a few carinated bowls from Pompeii which can definitely be dated before 79 A.D.. (Newby, 11) Another famous piece of evidence dated to the 1st century B.C. is a wall-painting in the House of Oplontis, in the Bay of Naples, which depicts a clear blown glass bowl filled with fruit. (Tait, 64) Probably with time more sites of ancient glass blowing houses will come to light, and possibly give the world some manuscripts to help us better understand the actual process of glass blowing.
Because there are no ancient sources that describe the process of glass making I will define some terms before explaining my area of specialty, glass blowing. For glass blowing I will use comparative evidence from a recreation of a glass house in Colonial Jamestown. Glassmaking is a highly specialized trade that has many technical terms associated with it. To better understand all of the advances that were made during the Roman Empire as a result of the discovery of glass blowing we must first get a general understanding of the different techniques and terms of glassmaking, (these are the words in bold print.) The earliest glass vessels in the pre-Roman world were Core-Made perfume flasks. The cores were made out of clay which would later be dug out. The pieces were very small and expensive , usually only used by the very rich for such luxery items as perfume. The process making a core-made vessel is as follows, "They were made on a solid core, possibly by dipping the core into molten glass, or by winding glass threads around it. The vessels were then fashioned by Marvering- rolling on a flat surface." (Hayes, 5) About 1700 years later in Hellenistic times Mould glass appears, but this technique is not fully understood. "In general they would appear to have been cast in two-part molds, either by pouring molten glass into preheated moulds, or by melting powdered glass within them." (Hayes, 16) Most of the pieces found came from southern Syria, the main center for the production of moulded bowls. A more specialized subgroup of mould-made glass is Mosaic Glass. "The normal method of manufacture of this kind of glass consisted of arranging rods or pieces of prefabricated rods of glass in different colors side by side either over or inside a mould, and then heating it until the glass fused together." (Hayes, 22) There are many subgroups of mosaic glass, one of the most famous being the millefiori from Venice. The following pictures and most of the text has to do with Blowing- the technique of forming an object by inflating a glob of molten glass gathered on the end of a hollow iron tube, or Blowpipe. (Harden 1st, 303) There aren't any ancient records or depictions of the dimensions a blowpipe, but from comparative evidence in Jamestown, blowpipes are approximately 4.5 feet (53 inches) long, and the diameter is about one inch.
Working Hole and Blowpipe
In Jamestown the furnace is heated to about 2000 degrees Fahrenheit using combustible gases rather than wood. The working hole is where the glass is kept until the artist removes a gather of glass onto the blowpipe. A gather can weigh anywhere from about half a pound to two pounds depending on the size of the object being made. After pulling the gather from the furnace a small amount of air is blow into the molten glass. At this point the gather is rolled across the Marvering table to help make sure the piece is symmetrical, and a tool that has been dipped in water is run along the outside as it is being turned to help with the shaping. Modern marvering tables are made out of metal, but there is no distinct evidence to indicate what they were made out of in antiquity. The similarity between the word marver and marble make a good argument to support the common thought that the table was indeed made of marble, but there is no evidence to back this up, so it is just conjecture.
Marvering
Shaping
Then the glassblower will blow through the pipe again and expand the piece more. If the glass has gotten too cool to work properly then it can be held in the glory hole, which is kept at about 2500 degrees Fahrenheit, until it is reheated.
Glory Hole
It is at this point that a pontil rod can be stuck onto the bottom of the vase or drinking glass to facilitate making a rim, or rolling the cylinder of blown glass over a rod on the marvering table. The rolling of the glass over the rods on the table will determine the basic shape of the vessel. by making indentions where it is being impressed by the rods. It can change a drinking glass into a flower vase in less time than it takes to read this sentence.
forming the rim with Forceps: other tools pictured
There are also many different tools such as shears, pliers, and forceps which can be used to form different shapes in the glass while it is hot. The glass can actually be cut very easily and with great precision with shears. After the basic shape of the object is finished then a rim, foot, or handle can be added on and fused with the hot glass. When the vessel is finished and the pontil broken off then the glass can be Annealed cooled slowly so it doesn't shatter, in a Lehr- a long low oven kept at about 800 degrees Fahrenheit.
Lehr used for Annealing
The piece of glass that I watched made was a single color vase with out any attachments such as handles. is seen here almost complete.
"Virtually all the present techniques of glassmaking in use today were known to the ancients. The tools have not changed essentially since the discovery of glassblowing, although on a technical level furnaces and chemistry have been improved." (Merrill, 14)
One of the things that has interested me the most are the different chemicals that are added to glass to change the color. In Jamestown Pam Rossmen explained how glass is colored in modern times, which is seemingly the same as several thousand years ago. The natural color of glass is green or greenish-blue because there is iron oxide in the sand. To get clear glass manganese is added, but if twice the amount is added then you get purple glass. For blue glass add cobalt, for red glass add copper or gold dust. This made red glass very expensive in ancient times. For yellow glass add silver, and for white glass add tin. If you add too much of any color or chemical element then you get black glass. Hugh Tait explains how colored glass was made in antiquity, but he does not give any sources to back up this knowledge so I am hesitant to believe that he has concrete proof.
Coloured glass was made by the addition of specific metal oxides and by varying the furnace conditions. For example, in antiquity copper produced turquoise or pale blue, dark green, ruby red or opaque dark red, while the addition of cobalt resulted in a deep blue; manganese was required for yellowish or purple glass, antimony for opaque yellow (or pale orange) and opaque white, and iron for pale blue, bottle green, amber or a dark color appearing black... Almost colourless glass could be achieved by the careful selection of fine silver free sand, but manganese and, it seems, above all antimony, the most effective agent, were used as decolourants. (Tait, 21)
There really are no exact formulas to obtain certain colors. There might be suggested amounts, but every batch is different. Changing the color of glass is a bit like cooking: everyone can follow a recipe, but true talent comes through when the artisan steps away from the norms and is willing to experiment. Today we have a recipe for glass that has been dated between the fourteenth and twelfth centuries B.C., preserved on a clay tablet from Mesopotamia. One of the most intriguing aspects of this tablet is that it gives instructions on how to add lead, copper and antimony in differing proportions to batches of raw glass; presumably this was used to change the color of the glass. (Tait, 8)
ancient clay tablet
Glass: Shiny, hard, fragile - shattering in an instant or surviving for thousands of years-a rigid liquid that is worked in a molten state- too hot to touch, but often made by hand- molded, blown, cut, engraved, enameled, or painted. Of the craftsman, it demands the ultimate in steady nerves, skill, control, judgment ,and spontaneity. (Zerwick, 8)
Maybe once you learn a little about the making of glass you begin to see all of the seemingly limitless possibilities of what can be formed; and hope that by mastering it you can bring out all of the attributes that are hidden within yourself. People have been fascinated by this for centuries. The thought of having a highly prized skill which would allow you to go where the wind blew you is a dream to me. So many aspects of glass blowing appeal to me, but when I read that the artists get to pick up and leave when they get the urge, it reaffirmed the thought that I must learn glass blowing. The mystique of a glass blowers' life is very enticing; I would like to be dexterous, creative, and spontaneous, and with all of these skills be able to make glass art work that might survive for centuries. The dualistic nature of glass is enticing because it mirrors all the different facets of human nature.
By melting together some very abundant, and usually extremely accessible materials like sand, ashes (alkali)- usually made by burning seaweed or other organic substances, and lime, from crushed stone, an amazing product was formed that changed the course of technological history. (Zerwick, 8) No one person is credited with the discovery of glass blowing, but the result of this invention has had enormous far reaching consequences because it drastically reduced the time necessary to produce glass objects. Glass is a very seductive material. Today we see glass everywhere we look, it is used in many different aspects of our lives. Yet every once in a while if you take the time to stop and really look at a magnificently blown piece of glass you can see the unbelievable beauty that can be captured in a molten liquid.
Daumas, Maurice. A History of Technological Invention. New York: Crown Publishers, 1969
Edwards, Charleen K. A Survey of Glassmaking- From Ancient Egypt to the Present. Chicago: The University of Chicago Press, 1974
Harden, Donald B. Glass of the Caesars. Milan: Olivetti, 1987 `
Harden, Donald B. Greek and Roman Glass I. London: British Museum Publications Ltd., 1981
Hayes, John W. Roman and Pre-Roman Glass- in the Royal Ontario Museum. Toronto: Hunter Rose Co., 1975
Merrill, Nancy O. A Concise History of Glass. Princeton: Village Craftsmen, 1989 |
Newby, Martine and Kenneth Painter, Roman Glass - Two Centuries of Art and Invention. London: Burlington House, 1991
Tait, Hugh. Glass 5,000 Years. New York: Harry N Abrams Inc., 1991
Robertson, R. A. Chats on Old Glass. New York: Dover Publications, 1969
Whitehouse, David. Glass of the Roman Empire. New York: Corning, 1988
Zerwick, Chloe. A Short History of Glass. New York: Corning, 1980