This method held a pre-eminent position in glassforming ever since its introduction in the middle of the first century B.C. until the late nineteenth century and is still widely used nowadays as a glassforming technique.
The process of free-blowing involves the blowing of short puffs of air into a molten portion of glass which is gathered at one end of the blowpipe. This has the effect of forming an elastic skin on the interior of the glass blob that matches the exterior caused by the removal of heat from the furnace. The glassworker can then quickly inflate the molten glass to a coherent blob and work it into a desired shape. The Toledo Museum of Art attempted to reconstruct the ancient free-blowing technique by using clay blowpipes.
The result proved that short clay blowpipes of about 30-60 cm facilitate free-blowing because they are simple to handle, easy to manipulate and can be re-used several times. Skilled workers are capable of shaping almost any vessel forms by rotating the pipe, swinging it and controlling the temperature of the piece while they blow. They can produce a great variety of glass objects, ranging from drinking cups to window glass.
An outstanding example of the free-blowing technique is the Portland Vasewhich is a cameo manufactured during the Roman period. An experiment was carried out by Gudenrath and Whitehouse with the aim of re-creating the Portland Vase.
A full amount of blue glass required for the body of the vase was gathered on the end of the blowpipe and was subsequently dipped into a pot of hot white glass. Inflation occurred when the glassworker blew the molten glass into a sphere which was then stretched or elongated into a vase with a layer of white glass overlying the blue body.