Cup of tea. Image 4 of 4. Thermogram of a hand dipping a biscuit into a cup of tea. The colours show variations in temperature. The scale runs from white (warmest), through yellow, orange, red and purple to blue (coldest). Thermography records the temperature of surfaces by detecting long-wavelength infrared radiation. The biscuit is seen to absorb the hot tea and take up some of the heat, in contrast to the undipped part. The heat of the tea is also seen showing the level of the tea inside the cup. The handle remains cool as it has little contact with the hot surfaces. For a sequence of thermograms showing a cup of tea being made, see images H584/103-106.