Bead and Glass Manufacture

There are many different ways to manufacture both glass and glass beads and similarities in manufacture could point to a transfer of technology from one region to another, whereas differences would suggest independent development.

Very few scholars have conducted studies on the different types of glass and bead manufacture.  Consequently, when archaeologists dig a potential manufacture site, they are not able to easily distinguish between materials used for one kind of manufacture over another.

METHODS OF MANUFACTURE

The following is a brief description of the methods by which glass and glass beads are made and how this process appears in the archaeological record.

Glass Manufacture

There are three general steps in glass manufacture.  First, the two primary components, silica and an alkali, are brought together and moderately heated for several days.  The substances are not allowed to melt, but react to form a solid, dark mass called “frit”.  This frit was then ground up as finely as possible in order to ensure the most thorough mixture.  Lastly, the powder was melted and could then be cast into glass objects.  Colorants are often added, but most scholars do not specify when or how.

Most glass is manufactured from silica sand, soda ash, and limestone.  However, glassmakers can obtain silica through quartz and sandstone as well.  In India, glass was generally made from pounded quartz.  Since quartz contains more silica than then sand, Indian glass often has a higher silica content than other ancient glasses.  Copper, iron, manganese, tin, and antimony are often used as colorants, and most colors can be achieved through the use of only iron and copper.

Drawn Bead Manufacture

There are many types of bead manufacture, but the two methods I will discuss here are for the general types of drawn and wound beads.  Both descriptions come from modern bead-making centers in India.  For drawn beads, glass cakes are first broken up and placed in a trough in the furnace.  The glass is heated for about two hours.  Two men then pick up the softened glass with a gedda paru, or a long iron rod about a meter long, and stir the glass.  They then remove the glass from the furnace and transfer it to the thin end of a lada, which is a long, tapered iron tube with the larger end about 10 cm wide.  The glass is rolled along the top of the wall near the furnace to eventually form a cone of glass.

Once a cone is formed, the men insert a cheatlek rod into the glass, which is an iron rod slightly longer than the lada with a bulbous end.  The cheatlek pierces the tip of the cone of glass, creating a perforation.  The entire thing is then placed back inside the furnace, where a master inserts a long-handled iron hook through the tip of the cone and pulls it towards himself.  After he has pulled the tubing back about five meters, he drops the hook and continues to pull on the tube, breaking it every meter or so to form lengths of glass tubing.  These tubes are then cut to the desired length of the beads.  The beads are then packed into ash and placed in a kiln where another man stirs them until the edges have rounded off.  The beads are then sorted, strung, and sold.

It is possible that this exact form of manufacture was not occurring in the last centuries BC, but scholars have compared the wasters from Arikamedu with those at Papanaidupet and says that it is likely that something similar took place at drawn bead manufacture sites in the past.

Wound Bead Manufacture

There are two general techniques for making wound beads: lamp winding and furnace winding.  Lamp winding requires a lamp, blowtorch, or other form of small, concentrated flame, and so was probably not practiced in antiquity.  Furnace winding, however, is much more likely.  Up to two colors of glass are heated in a crucible in a furnace.  The glass is not allowed to melt, only to soften, and so the two colors do not mix in the crucible.  The bead-maker inserts a mandrel, which is an iron rod about a meter long, into the glass.  The worker then takes the mandrel out and twists it so that the glass fully surrounds the mandrel.  The bead is knocked off during a short period when the iron cools and contracts faster than the glass.  The beads are packed into an ash-filled pot and placed in sunlight, allowing the beads to cool slowly, ultimately strengthening the beads in a process called annealing.  The beads are then sorted by size and color, strung, and sold.

ARCHAEOLOGICAL REMAINS OF MANUFACTURE

Given the different methods for the production of glass and beads, there are differences in the materials, tools, and waste produced in the process.  Those discussed below are things that we might expect to find in the archaeological record at a glass or bead-making site.  The potential finds have been separated into three general categories: raw materials, tools, and waste.  Within each of these categories, they have been divided into those specific to glassmaking, those specific to drawn bead-making, and those specific to wound bead-making.

Types of archaeological material found at glass or bead manufacture sites.

Organic Inorganic Ceramic Glass Metal
Ash Silica sand Crucibles Chunks Lada
Iron Polishing bucket Wasters Gedda paru
Cobalt

Copper

Kiln

Furnace

Storage jars

Annealing potsFragments

Finished objects

FritMandril

Blowpipe

Bellowpipes

Blades

Mala

Sieves

 

Raw Materials

As stated earlier, the primary ingredients of glass are silica (which is obtained from silica sand, quartz, or sandstone) and an alkali (often soda or potash).  The alkali lowers the melting point of the silica so that the ancient furnaces could actually melt the substance.  The reaction between silica and the alkali is not stable, however, and so lime was needed to stabilize the reaction.  Many believe that ancient populations probably did not know this vital fact, since lime was often an impurity in the silica sands.

As far as raw materials, then, glassmakers needed one from each of the above categories.  The sources of silica have been discussed already.  Soda is often obtained from reh (north India) or sondu (south India) soil, which is gathered by collecting water in plots of land and then allowing the water to evaporate over four or five days.  The soil becomes encrusted with flakes of soda which are gathered and mixed with other ingredients to make glass.  Potash comes from various plant ashes and saltpeter, which is found in many places throughout India.  Colorants came in the form of copper, iron, manganese, tin, and antimony, which were found in various forms.

If a site were making glass on a large scale so as to be further processed at the site or traded elsewhere, then we would expect to find at least some indication of these materials at the site.  It would be foolish to say that all glassmaking sites must have evidence of the raw materials, especially since the materials have probably deteriorated over time.  It is likely, however, that many glassmaking centers were located very near to deposits of at least some of the raw materials, especially those of silica.  Evidence of these materials at or near the site would be strong evidence of glass manufacture.

For bead-making sites, however, the raw materials are far less distinguishable because they are the finished product of the glass manufacture.  Modern bead sites in India often obtain chunks of either raw or colored glass from elsewhere and reheat it to use for beads.  Since the finished product of a glass manufacturing site is the raw material of a bead manufacturing site, we must rely on other means of determining the type of industry present.

Tools

Bellowpipes, blowpipes, and crucibles are common at modern glassmaking sites and appear in some quantity at ancient manufacture sites.  These materials are also common to bead-making, but in different sizes and quantities.  For example, crucibles are used in both glass and bead-making operations are of two different sizes, the glass crucibles being larger.  During the glassmaking process, however, the glass that has been created is allowed to solidify in the crucible and is removed by breaking the container.  Thus, at glassmaking sites, there ought to be large numbers of broken crucibles, since new ones were made for each chunk of glass created.  Evidence of storage containers would also be expected, but this is a topic rarely discussed in the literature.  This discrepancy is likely due to a lack of storage containers found at the sites, though some have been found in the Pandanan shipwreck and at other sites.

We expect a different range of tools at beadmaking sites.  At sites making drawn beads, we would expect to find some evidence of the lada’s along with the blades used to cut the beads.  At sites making wound beads, we might find the wires or mandrels that the beads were wound around, the crucibles used to hold the glass, and the mala used to strike the beads off the mandrel.  Bead-making crucibles are more likely to be whole, since there is no need to break the crucible after every use, and there are likely to be fewer than at a glassmaking site.  Crucibles may also have more than one color of glass in them, since they were large enough to fit two bodies of glass without intermixing.  At bead-making sites in general, we would expect to find any combination of polishing buckets, paddles, sieves, and annealing pots, though perhaps not in the same general places.

The furnace is also a clear indication of manufacture.  Furnaces differ in appearance and make based on whether the furnace is used to make glass or beads. Some scholars provide detailed descriptions of some modern sites, which could give an idea as to the structure of ancient glass and bead furnaces.  Furnaces differ not only between glass and bead manufacture, but also between subtypes of bead manufacture.  Thus, a wound bead furnace is quite different from a drawn bead furnace.  Extensive study of furnace styles has not been conducted, but such a study would certainly aid in the identification of manufacture sites.

Furnaces appear at both bead and glassmaking sites, but the kiln is specific to bead-making, specifically drawn beads.  At modern bead sites, beads are packed in ash and moved to a kiln after they have been cut to the desired length.  Here, they are stirred for about 20-30 minutes and reheated so as to round the edges of the beads.  They are then sorted according to size and color.  Evidence of a kiln in an archaeological site, then, could provide evidence for a drawn bead manufacturing center.

Many of the tools are common to both glass and bead manufacture, yet there are plenty of tools specific to each type.  Any evidence of these tools would allow archaeologists to type a manufacture site and provide some information about the structure of production in the region.

Waste

Finally, there should be evidence of waste at a manufacture site.  Much of the waste for glassmaking is common to bead-making sites as well, but there are certain exceptions.  In general, it seems that a presence of glassmaking waste and a lack of bead-making waste could point to a glass manufacturing site, but a lack of evidence is not truly evidence.  Waste for glassmaking consists of slag, chunks of glass, frit, or glaze.  Glaze is a glassy layer applied a base of some other material.  While it is possible for glaze to be used at a bead-making site, it is much more likely to be found at a glassmaking site, as is slag.  Chunks of glass can occur at either because chunks were likely traded between glass and bead manufacture sites.

For wound beads, waste products do not consist of much more than drips and splatters of glass, broken or cracked beads, and ash from the annealing buckets.   Chunks of raw glass might also be present, but this is more of a raw material than a waste product.  It is important to note here that while many scholars like to attribute the presence of glass splatters to glassmaking, they are produced whenever glass is worked, which could be either during glassmaking, bead-making, or some other glass-related manufacture.  Glass can splatter whenever it melts, and so splatters only indicate possible manufacture of something relating to glass, not manufacture of glass itself.  It should also be noted that in many cases, broken or cracked beads were not remelted to form new beads because the color would not be uniform.  Thus, waste was not recycled unless a mixture was desired.  This was observed at a modern wound bead manufacture site, but it is possible that the same occurred in the past, which would lead to a relatively large amount of bead waste at wound bead manufacture sites.

Drawn beads, on the other hand, produce quite a few wasters specific to their method of manufacture.  Pieces of glass fall of the gedda paru after the glass has been thoroughly mixed, glass falls off the hook after drawing out a tube, patches of glass fall off the lada once all the tubes have been drawn, and any number of mistake tubes would also be left as waste products.  Other shapes, such as horns and twisted tubes, are also characteristic of drawn bead-making.  Splatters and drips also occur at drawn bead manufacture sites.

One reason to examine differences in waste products is that many sites yielding possible evidence of glass working do not have strong claims for manufacture.  Waste occurs at every step of the process, whether it is in the manufacturing of the glass, the forming of the bead, or the stringing of the final product.  Research of modern bead-making centers demonstrated that all of these steps rarely occur in the same location; the glass is often made at a separate site from the beads and the beads are often strung only after they have been purchased.  This means that debitage from stringing is found in places that have little involvement with the manufacture of the glass beads.  Thus, when a report mentions “wasters” or “unfinished beads” as evidence of manufacture, they should be treated very cautiously, since wasters and unfinished beads are not a true indication of manufacture.

This is not meant to be an exhaustive list of the potential remains left at glass and bead-making sites.  It is meant to provide an overview of the general types of evidence we might expect to find.  It should be noted, however, that so little research has been done on each of these topics and evidence of the artifacts and features mentioned here are so seldom mentioned in archaeological contexts that any analysis of these materials is greatly hindered by the lack of reported data.  A good example of this lies in the different types of furnaces present at a manufacture site.  According to ethnoarchaeological research, the furnaces for glass, wound bead, and drawn bead manufacture differ markedly in their appearance and use.  However, since archaeological reports often only describe the existence of a furnace and not the structure of the furnace, we are unable to compare ancient furnaces with the models recorded in ethnographic data.  It is true that the number of glass or bead furnaces found in archaeological contexts is relatively small, but the knowledge of the structure would provide much more information than is currently available

References:

Cayron, J. n.d. Comparative Analysis of Glass Beads Recovered from the Pandanan and Sungai Mas Sites: An Archaeological Understanding of Southeast Asian Trade. Southeast Asian Studies Bulletin.

Francis, P. 2002. Asia’s Maritime Bead Trade: 300 BC to the Present. Honolulu: University of Hawai’i Press.

Kanungo, A. 2004. Glass Beads in Ancient India: An Ethnoarchaeological Approach. Oxford: BAR International Series 1242.

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About Heather Christie

Heather is an archaeologist, photographer, and writer whose research focuses on beads and bead trade, particularly in a maritime sense. She's currently working working on a PhD in Digital Design (focusing on heritage visualisation) at the Glasgow School of Art.
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