The Fine Art of Glassmaking: History and techniques

There is a variety of ancient glass making techniques, such as casting, core forming, mosaic, inflation, mold blowing, cameo carving, incising, and cutting.  All these techniques are still used by glass artist today.

Three main ingredients of ancient glass are silica, from beach or river sand; soda (sodium carbonate),
found in the mineral natron and in the ashes of certain plants,  and lime, from seashell debris in beach sand. When heated to at least 1300 degrees F, these elements melt together to form glass. While in a molten state, glass is manipulated in a variety of way to create vessels. 

Casting and Core Forming

The earliest know glass objects date to about 2500 B.C. and was found in Mesopotamia (present-day Iraq and western Iran).  They were made by casting in an open old or by core forming, a technique in which a ceramic-like core formed around a metal rod was encased in glass. These processes were used for more than 1,500 years.


Mosaic Glass

Like a mosaic made of stone, mosaic glass is comprised of a number of small pieces, sliced from canes (rods) of glass. Canes could be multicolored, formed from rods of different colors, which were fused together and manipulated into patterns. Ribbon glass were created by fusing lengths of cane placed side by side. Marbled glass was fashioned from multiple colors that were melted to mimic veined and banded stones such as marble and agate.

Inflation

In the mid-first century B.C., glassmakers in the environs of jerusalem discovered that molten glass could be inflated into a bubble at the end of a hollow tube.  This blowing technique revolutionized the
glass industry. The process allowed vessels to be make quickly and less expensively, and in the first century A.D. glassware began to replace clay vessels for household use.

Mold Blowing

Toward the end of the first century B.C., vessels were manufactured by inflating glass into molds. Mold-blown objects were decorated in relief with the designs carved into the molds, which were made either as a single piece (a dip mold) or in multiple parts— some had up to six panels, plus a base section. The materials used to construct molds include stone, clay, bronze, and plaster. Molds were reused, and it is possible to determine which vessels were produced in the same mold by taking precise measurements.

Decorating Blown Glass

Various techniques were employed to embellish inflated glass vessels. Pincers and tongs were used to pinch, pull, or push the glass into different shapes and designs.  Trails of glass were often wound around the body to created snakelike patterns and to add handles, rims, and feet. Splashware was created when a vessel being formed was rolled into multicolored chips that fused to the body and expanded during inflation. Cut and incised decoration, done after a vessel had colored, ranged from sharp, overlapping facets resembling carved rock crystal to inscriptions and pictorial scenes composed of thin linen.

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