Place a safety pin on a sheet of paper. Hold the sheet over a burning candle, until the paper becomes yellow and charr. On removing the pin, its white trace is observed on the paper. Why?
The safety pin is made of steel which is good conductor of heat. So, the safety pin takes heat from the paper under it and transfer it away to the surroundings. The portion of the paper under the safety pin remains comparatively colder than the remaining part.