Page 29 - Curriculum Visions Dynamic Book

Glassmaking instructions
People treasured their skills at making glass. From time to time they wrote down instructions about how to make glass, which we can still read today.
Early glassmaking had little science to help it, and so it was a mixture of luck, skill, and trusting in the gods.
In fact, more attention is given to pleasing the gods than to preparing the glass mixture.
Glassmaking instructions begin by telling people to choose a favourable month and then look for a good omen.
Only then should the furnace be built and blessed by putting religious objects near it. To make sure the glass is even more likely to be good, sacrifices of sheep should be made, incense burned, and an offering of honey and butter put out for the gods. After this has been done, the fire can be lighted.
Special wood should be chosen for the fire, for example, poplar wood without its bark.
The glass mixture should be of finely ground quartz and plant ashes. Once it has been made up, the fire can be started. Once the mixture turns yellow, it is ready to be poured out.
Whatever the first discovery, from this time on, for thousands of years the raw materials for making glass were the same – a mixture of sand, wood (the source of soda), and crushed seashells – the source of lime.
Crucible glass
Soon people learned that glass could more conveniently be made in a crucible – a dish made out of clay that could be put on a fire. But an open-topped crucible will not allow temperatures to get high enough for glass
to form properly. Furthermore, the natural materials in clay contaminated the glass with other chemicals. As a result, pure glass, and especially clear glass, could not be made. This was a problem only solved in later centuries by using extremely pure materials.
Because glass is difficult to make, people began to specialize: Some operated furnaces and made the glass in bulk; others took the raw glass and reheated it and fashioned it into finished goods.
You can get an idea of the scale of this glassmaking from the slab of glass preserved at
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