When the glass cooled off, the clay was chipped out of the inside leaving just the hollow glass vessel.[3] This glass was very thin as the fire was not as hot as modern day furnaces. The blowpipe was invented around 1 B.C. This allowed molten glass to be gathered on the end of the blow pipe and blown into the other end to create a hollow vessel. Eventually, the use of a mold was introduced, followed by the invention of a semi-automatic machine called the Press and Blow.