Cooking on a gas stove. Thermogram of soup being heated in a pan on a gas stove. The colours show variations in temperature. The scale runs from white (warmest), through red, yellow, green and blue to purple (coldest). Thermography records the temperature of surfaces by detecting long- wavelength infrared radiation. The blue of the pan and the soup show good heat conduction by the pan (probably made of metal). The spoon (probably made of plastic or wood) is a poor conductor and stays purple. The intense heat of the gas flames is seen under the pan.