Glassmaking Techniques

		Core Forming and Casting
		Mosaic Glass
		Inflation
		Mold Blowing
		Decorative Techniques

	Core forming a glass vessel
	Video: Watch a glassmaker core-form a vessel. (2:05)

Core Forming and Casting
Core forming and casting are the oldest known glassmaking techniques. In core forming, glassmakers mold clay or dung around a metal rod to create a core in the shape of a vessel. They then cover the core with molten glass to create the vessel, as shown at right.

Glassmakers can then add different colors of glass to make decorative stripes and drag a pointed tool through the stripes to create a zig-zag pattern.

After the glass cools, glassmakers grind the clay out of the vessel.

In casting, a glassmaker makes a vessel by pouring hot glass into a mold. He or she lets the vessel cool, then removes any excess glass with a cutting wheel. He or she might also use the wheel to incise decorative patterns into the vessel.

	Slicing glass canes to make mosaic glass
	Video: Watch a glassmaker create a mosaic glass vessel. (2:50)

Mosaic Glass
Mosaic glass is made from many small pieces of glass sliced from rods, or canes, of glass.

Glassmakers fuse the slices into a disk of hot glass, then place the disk over or into a mold.

Ribbon glass is made from lengths of cane placed side by side.

Marbled glass is made from multiple colors of glass that are heated and melted together to form patterns similar to layered stones like marble and agate.

	Preparing glass for free blowing
	Video: Watch a glassmaker free-blow a vessel. (1:59)

Inflation
Somewhere in or around Jerusalem around 50 B.C., glassmakers discovered that they could inflate glass into a bubble at the end of a tube.

This new glassblowing technique, known as inflation or free blowing, allowed glassmakers to produce vessels so quickly and cheaply that glass vessels began to replace clay ones for household use.

	Removing glass from a two-part mold
	Video: Watch a glassmaker mold-blow a vessel. (1:47)

Mold Blowing
One variety of inflated glass is known as mold-blown glass. Glassmakers create decorative vessels by blowing glass into a mold containing incised designs. They can use a single mold or a mold with several parts, one for each segment of the vessel.

Ancient molds were often made of bronze, clay, plaster, or stone. The earliest designers of glass molds were probably ceramists (potters) who had experience making molds for clay vessels.

Decorative Techniques
Glassmakers decorate vessels using a variety of tools and techniques.

They use pincers and tongs to pinch, pull, and push hot glass into different shapes and patterns. They wind glass around a vessel to create snakelike patterns and add handles, rims, and feet.

To create a special kind of decorative glass known as splashware, glassmakers roll a vessel in multicolored glass chips, reheat the vessel, and then further inflate it to stretch the chips across the surface to look like splashes of color.

Glassmakers also ornament glass vessels after they cool by painting them or using a lathe and cutting wheel to form decorative patterns. Painted glass vessels are rare, and none have survived with their pigments intact.