Glassmaking techniques

Glassmaking in the Ancient Near East began in the mid-second millennium BCE and from there quickly spread to Egypt. Ancient glass was made of silicates (quartz, quartz sand), an alkaline flux and lime.

The lime was vital as it prevented the glass from remaining water-soluble — a fact that at the time was apparently unknown, since scientific studies of ancient glass have found no deliberately added lime. Presumably it was mixed in by chance, whether in the form of sand contaminated with splinters of shell or through the addition of lime-containing plant residues. Metal oxide was also added to colour the glass.

Until the first millennium BCE, glassmakers were only able to produce opaque glassware, some of which looks as if it were made of gemstone. The first hollow vessels were produced using a core of organic material and perhaps sand. The technique used to make them is still the subject of debate; they may have been created by dipping a rod wrapped in strips of cloth into hot molten glass and later removing the core. Glassware moulded around a core, albeit produced in a slightly different way, experienced a boom in the eastern Mediterranean beginning in the seventh century BCE.

Other methods were developed over the years. The 'lost wax' method of casting, for example, worked for glass as well as metal, or discs of hot glass could be laid over a mould. This allowed larger hollow forms to be made, among them the 'ribbed bowls' so popular in the first century BCE. Their manufacturing technique is still the subject of controversy: It is possible that the makers first made a round glass disc and then, using tongs, pressed the ribs down onto the obverse while it was still hot. The other side of the disc was then laid over a hemispherical mould and reheated in order to mould it to the form, producing a bowl shape. This technique permitted relatively rapid production.

The ribbed bowls belong to the same tradition as the variants decorated with tongues radiating out from the base, which had been produced in ceramic, metal, and - more rarely - cast glass ever since the Persian period (fifth-fourth century BCE). The glass of these bowls is no longer opaque, but rather translucent and almost colourless. Since vessels made of costly rock crystal were available on the market at the same time, it seems reasonable to conjecture that these new, almost transparent objects were intended as inexpensive imitations.

This Parthian bowl of greenish-blue, almost transparent glass comes from northern Iran. The colour is due to contamination of the silicate with metal oxide and was not deliberate. The shape of the ribs on the underside of the bowl is typical of the Roman era, which overlaps with the Parthian Period. The bowl undoubtedly served as a drinking vessel for the elite.

The glassmaker's blowpipe was invented in the Levant only in the first century BCE. After a century or so of experimentation, this implement made it possible to quickly produce vast numbers of large, thin-walled vessels. In his Natural History, the historian Pliny the Elder (23-79 CE) reports at length on glassmaking in this region. From there it spread throughout the ancient world, ushering in a new era of glass art. 

The above is a lightly edited version of part of a chapter entitled, ‘The Parthian and Sasanian Empires’ from a book entitled, ‘IRAN: Five Millennia of Art and Culture’, edited by Ute Franke, Ina Sarikhani Sandmann and Stefan Weber, published by Berlin Museum of Islamic Art. The photo was taken from the book.