Blown mosaic glass
The Furnace Project 2015 was devoted to blown mosaic glass.
Mosaic glass is formed by fusing round chips to give the finished vessel a multicoloured pattern.
Most Roman mosaic glass vessels were produced by fusing chips to create a large disc, which was then lowered over a loam hemisphere or another mould (“slumping”).
Blown mosaic glass was made with the aid of a blowpipe, but exactly how it was produced had previously been unclear.
The steps in the process
The glassmaker used tweezers to stretch hot glass and produce a glass cane of the desired thickness.
To make patterned or multicoloured chips, he fused glass canes of different colours and stretched them again.
He then cut off small pieces of the cane to make the chips (Images 1 and 2).
The chips were carefully warmed on a surface.
By attaching a small amount of hot glass to the blowpipe, the glassmaker was able to pick up the chips, gathering a few at a time (Image 3). During this process, he would need to keep on reheating the glass in the furnace.
Once the chips had fused into a sphere, the glassmaker inflated it with the pipe (Image 4).
To shape the rim, the vessel had to be picked up from the other end:
the glassmaker attached an iron rod known as a “punty” to the glass and broke the pipe off on the opposite side. He would then shape the rim with tweezers and another implement (Image 5).