Ancient Methods. Shaping hot, molten glass
into useful articles has long been a challenge. Molten glass is extremely hot, caustic, sticky, and difficult to handle. In the period extending from about 2000 b.c.e. to 50 b.c.e., there were three basic methods used to form glass. One of the earliest and most widely used was core forming. This involved distributing molten glass around a clay core on a metal rod. The rod with the clay core could either be dipped into molten glass, or the hot liquid glass could simply be poured over it. The outer glass coating was then rolled (marvered) on a flat stone surface to smooth it. Often the object was decorated by dribbling more glass, sometimes of a different color, onto its surface. The hot glass was then annealed (cooled slowly so as to relieve thermal stress), and the metal rod was removed and the clay core scraped out.