Obsidian is formed when molten rock from a volcano cools slowly.

The main ingredients in making glass is heat and ____.

By the ____ many European cathedrals were being decorated with stained glass windows.

Mirrors were invented in the 16th century in ____.

In the ____ century in Northern Italy the first glasses to enhance eye sight were invented.

Reading glasses use ____, which is the way light bends as it passes through transparent surfaces.

Recycling glass dates back to the ____ Empire.

There are 40 recycling centres in metropolitan ____, with 120 across the state.

In Australia, around ____ of all glass products come from recycled glass.

What chemical compound is glass usually made from?

Hans Lippershey invented the telescope in ____.

Fibre optics are ultra-thin strands of ____.

Fibre optics work via a ____ process.

A 1200 degree furnace is known as a ____.

Glass is something called an amorphous solid.

Glass blowing is using glass in its soft, molten form and using ____ equipment like blow pipes.

The world's most famous glass blowers were from the island of Murano in ____.

The filament of a light bulb is made of ____.

The inventor of the light bulb was ____.