All That Gleams
by Bob Brooke

The Romans used more glass than any other ancient civilization. In 63 BCE, they conquered the peoples of the Eastern Mediterranean and returned to Rome with skilled glass makers, making Roman glass over 2,000 years old.

The Romans used glass in nearly every part of their daily lives. Small boxes and bottles held toiletries, cosmetics, oils, medicines, herbs, and perfumes. Merchants and traders packed, shipped, and sold food products and other goods across the Mediterranean in glass bottles and jars of all shapes and sizes. Later, colorful sparkling glass bowls and beakers holding wine, fruit, and herb-infused olive oils graced dinner tables.

The Romans used glass primarily for the production of vessels. Using the glass making techniques of the Hellenic Greeks, they originally concentrated on the production of intensely colored cast glass vessels. However, during the 1st century CE, colorless or “aqua”' glasses became dominant.

Despite the growth of glass working and the growing place of glass in Roman life, there was still no Latin word for it in the 1st century CE.

Glass Making
Most Roman glass making techniques were time-consuming, and the initial product was a thick-walled vessel which required considerable finishing. This, combined with the cost of importing natron for the production of raw glass, contributed to the limited use of glass and its position as an expensive and high-status material.

Glassmakers produced glass by core forming, casting, cutting and grinding. But it was an expensive process, so only the wealthy could afford it. With the invention of glass blowing around 50 BCE, glass instantly became available to everyone. The Roman glass industry rapidly developed over a couple of generations during the first half of the 1st century CE. Glass vessels became commonplace throughout the empire. And the Romans even exported them to Scandinavia and the Far East.

Roman glassmakers used sand, alkali, sodium carbonate, and metal coloring agents to produce raw glass. Eventually, it became a high art, producing items in a large range of colors, patterns and complex techniques. They used copper to make turquoise to light blue, green, or red colored glass. Adding cobalt created dark blue glass. Glassmakers used manganese and antimony to make the glass yellow, white, and purple. Iron made a light blue, green, brown and black. Glassmakers chose a wide assortment of colors to simulate the colors of gemstones, such as lapis, amethyst, and turquoise.

Roman glass production relied on the application of heat to fuse two primary ingredients—silica and soda. Glass workshops could produce tons of raw glass in a single furnace firing, and although this firing might have taken weeks, a single primary workshop could potentially supply multiple secondary glass working sites. Historians believe that raw glass production centered around a relatively small number of workshops, where the Romans produced glass on a large scale, then broke it into chunks.

Glassmaking required fuel in large quantities, sources of sand which represented the major component of the glass, as well as natron to act as a flux. Since natron could be found only in the region of the Eastern Mediterranean, the Romans traded raw colorless or naturally colored glass which they produced for it.

Archaeologists believe that melting didn’t take place in crucibles but rather in cooking pots used for small scale glass operations. For larger amounts of glass, the Romans built large tanks or tank-like ceramic containers and in the largest cases, built large furnaces to surround these tanks.

Glass Working
The Romans separated glass making from glass working. Unlike the making process, the working of glass required significantly lower temperatures and substantially less fuel. As a result of this and the expansion of the Empire, glass working sites developed in Rome, Campania and the Po Valley by the end of the 1st century CE, producing the new blown vessels alongside cast vessels.

By the early-to-mid-1st century CE, the growth of the Empire saw the establishment of glass working sites at locations along trade routes, with Cologne and other Rhineland centers becoming important glass working sites from the Imperial period, and Syrian glass being exported as far as Italy. During this period vessel forms varied between workshops, with those in the Rhineland and northern France producing distinctive forms which aren’t seen further south.

Glassblowing allowed glass workers to produce vessels with considerably thinner walls, decreasing the amount of glass needed for each vessel. Glass blowing was also considerably quicker than other techniques, and vessels required considerably less finishing, representing a further saving in time, raw material and equipment. Although earlier techniques dominated during the early Augustan and Julio-Claudian periods, by the middle to late 1st century CE, earlier techniques had been largely abandoned in favor of blowing.

Glass vessel production reached its peak at the beginning of the 2nd century CE, with glass objects common throughout the Roman Empire. The primary production techniques of blowing, and to a lesser extent casting, remained in use for the rest of the Roman period, with changes in vessel types but little change in technology. From the 2nd century onwards styles became increasingly regionalized, and archaeological evidence suggests that bottles and closed vessels such as unguentaria, or vessels used to hold olive oil, moved throughout the empire as a by-product of the trade in their contents, and many appear to have matched the Roman scale of liquid measurement. The use of colored glass as a decorative addition to pale and colorless glasses also increased, and metal vessels continued to influence the shape of glass ones.

Decorative Glass Techniques
The Romans produced several patterns of glass. Floral, known today as millefiori, and spiral patterns: Glassmakers produced these by binding rods of colored glass together and heating and fusing them into a single piece. They then cut them in cross-section, and the resulting discs could be fused together to create complex patterns. Alternately, two strips of contrasting-colored glass could be fused together, and then wound round a glass rod whilst still hot to produce a spiral pattern. Cross-sections of this were also cut, and could be fused together to form a plate or fused to plain glass.

Glassmakers created marbled and dappled patterns by distorting the original pattern during the slumping of the glass plate during melting. However, by using spiral and circular patterns of alternating colors producers could imitate the appearance of natural stones such as sardonyx.

To produce lace patterns, glassmakers twisted strips of colored glass with a contrasting colored thread of glass before being fused together. Though this was a popular method in the early period, it appears to have gone out of favor by the mid-1st century CE.

By fusing lengths of monochrome and lacework glass together, glassmakers could create vivid striped designs, a technique that developed from the lace pattern technique during the last decades of the 1st century CE.

The Romans also produced enameled glass and engraved glass.

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