The Difference Between Free Blowing and Mold Blowing
There are two basic methods used in glassblowing. The first, and the oldest, is known as free blowing. In the method, the glassblower begins by placing a small amount of molten glass on the end of his blowpipe. Using a serious of short puffs, he forms a small bubble of air inside the glass. He is then able to blow larger and larger puffs of air into the blowpipe, expanding the molten glass until it is the approximate size of the finished piece. He can then use various tools to shape the glass as he blows into it. Those tools can include handheld tools, marble slabs, and even wet newspapers. He may return the glass to the furnace to reheat it, and can add other bits of glass to form handles and spouts.
On the other hand, mold blowing involves placing the end of the blowpipe and the molten class it carries into a mold. The glassblower then blows into the blowpipe, inflating the glass until it fills the mold. Molds can be made of plaster or wood, but are typically made of metal. No other tools are used. Mold blowing can be used to make multiple copies of a single design.