4: Thin & Hollow

Glass Blowing by Hand

Lampworking Glass Tube

Glass Blow and Blow Molding

Glass Press and Blow Molding

Plastic Blow Molding

Injection Blow Molding

Extrusion Blow Molding

Dip Molding

Rotational Molding

Slip Casting

Hydroforming Metal

Backward Impact Extrusion

Molding Paper Pulp

Contact Molding

Vacuum Infusion Process (VIP)

Autoclave Molding

Filament Winding

Centrifugal Casting

Electroforming

Hollow components with a thin wall section

The longest chapter in the book, this embraces all sorts of processes for forming hollow and, generally, thin-walled shapes. It discusses the many variations of blow molding, a process that has been used for several thousand years to produce priceless handblown glassware. The blow-molding principle has been successfully employed in industrial mass-production, especially by the plastics industry, which spews out millions of disposable bottles for the soft drinks industry. Other forms of casting and molding are included, from the very common rotational molding, a form of which is used to produce chocolate Easter eggs, to the less common centrifugal casting that hurls metal or glass around a rotating drum forcing the material to attach itself to the walls, to make anything from small pieces of jewelry to huge industrial pipes.

Glass Blowing by Hand

Product	Air Switch flask lamp
Designer	Mathmos Design Studio
Materials	acid-etched glass
Date	2004

Although this light was handblown, the straight sides and symmetrical shape were achieved by blowing into a mold. Usually, the shape of a handblown piece is controlled only by a series of hand tools (as illustrated in the photographs, right).

For at least two thousand years, this technique has been used to make anything from tableware to craft pieces. It involves blowing air through a metal tube to inflate a ball of gathered glass at the end of the tube. Before glass blowing, glass objects were produced by dipping a sand core in molten glass prior to rolling it against a flat surface to control the shape. Once cooled, the sand could be removed, leaving a hollow container. With the introduction of the blowing technique came a whole new set of possibilities, not only in terms of shape but also in terms of widening the availability of this material.

Today, hand-blowing is still used industrially to produce a whole range of products that are blown into molds, from lighting to wine glasses. Hand-blown glass constitutes a valuable bridge between mass-produced glassware, which requires expensive tooling and very high volumes, and individual one-off pieces.

1 A mass of molten glass is gathered onto the end of a steel tube, ready to be blown.

2 Various hand tools are used to shape the hot glass, in this case a stack of wet fabric.

–  Flexible enough to produce different shapes.

–  Can be used for one-off, batch, or medium-volume production.

–  Units can be expensive due to labor costs.