Demonstrating glass X-ray tubes, paperweight, and glass plate at an exhibition, 1946 PA-151342

Glass is a manufactured material formed when a mixture of sand, soda, and lime is heated to a high temperature and assumes a molten, or liquid, state. Unlike most other materials we produce, it does not form crystals as it cools. Instead, it becomes a "super-cooled liquid," behaving not unlike toffee and resisting any change in the arrangement of its molecules. This means that glass can be manipulated while hot to form any shape desired and will retain that shape as it cools. The hard, solid glass objects we are familiar with have all passed from a hot liquid state to a cold rigid one without changing structurally.

Hour-glass, Sandy Cove, Newfoundland CMC N-50

Paper weight promotional, advertizing the Luxfer Prism Company of Toronto CMC 983.20.3

What makes this substance both practical and beautiful? Glass is relatively easy to make, the raw materials are abundant and cheap, and it can be recycled and reused indefinitely. It changes little over time and is not affected by corrosive materials, even most acids. Glass does not react with its contents, it does not retain odours, and it can be completely sterilized. Liquids and air cannot pass through, but light easily penetrates it. Nor does glass conduct electricity. Glass can also be rolled, moulded, blown, and cast while molten, and can be made in any colour imaginable.

Jug, flint glass, 1880s, made by US and English glass works CMC D-2013