The famous North Rose Window at Notre Dame cathedral in Paris dates from 1250.
Most of us have heard the story: Medieval cathedrals have window glass that's thicker at the bottom than at the top.
That happens, we were told, because glass is a liquid at room temperature, and over the centuries, it slowly flowed downward.
But recently, scientists examined a sample of 20-million-year-old Dominican amber, a naturally occurring glass. They found that the structure of the amber did not change with stress or heat any more than a newer sample would. What's going on?