when a piece of red glass heated in a furnace is taken out, it glows with green light. Why?

Explanation

Red and green are complement colours. When a piece of red glass is heated in a furnace , it absorbs green light but transmits red light. When this piece of red glass is taken out, it emits green light, i.e., glows with green light. It is so because a good absorber when heated is a good radiator when cooled.