The oldest known method of glass making is known as core-forming or inner-mold forming. The most common form of mold or sand-core was prepared by using coal, sand or quartz and this core was attached to a piece of metal bar to handle the mold easily.

The core is pre-heated and inserted into the molten glass to be covered by the glass. Then a second bar is used to wrap the core which is already covered with the first thin layer of glass with extra fibres of molten glass.
After this, the surfaces are made glossy and freed from any irregularities by rolling the glass covered mold on a smooth surface.

Different colored glass fibres may be used to decorate the final object. Also by drawing figures and shapes on the soft surface of the glass object with special rakes or sharp metal pieces, early glass makers were able to decorate their items.

The mouth, the base and the handle are added to the object at a later stage. Finally, the mold is taken out of the glass object. It is now ready to go out of the workshop.

Another technique, called rod-mold was successfully used in ancient times to make small beads, delicate and tall cups.

The core-forming technique was first developed and used by the Mitanni kingdom in Mesopotamia as early as the 16th century BC.

Then it was widely used in Egypt and the east Mediterranean regions. During the last Bronze Age (1500 - 1200 BC), the most important glass production centers were in Egypt and Mesopotamia.

Even after the technique was abandoned by Egyptian glass makers in the 11th century BC, the Mesopotamian makers continued and perfected their skills.

In the 7th century BC the people of Rhodes and Italy learned this technique from Mesopotamians and continued to improve it.