As if glassblowing wasn't fast enough—it takes under three minutes to make a Roman bottle—cracking-off made the process even faster. This technique was well known by AD 20 or so, and cut the manufacturing time of simple tumblers in half.
The technique whereby glass is removed from the surface of an object by grinding it with rotating wheels made of stone, wood, and cork. The first stage of the process employs a stone wheel under a continuous stream of water. Later, wheels of fine-grained stone and wood, fed with various abrasives, are used to grind and polish the surface.