Making a cup of tea. Image 3 of 4. Thermogram of a hand pouring tea from a teapot into a cup. 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 heat of the boiling tea is seen inside the teapot and also transferring heat to the cup. The teapot has also left a heat shadow where it rested on the surface at lower right. The handles of the cup and teapot remain cool due to little contact with the hot surfaces. For a sequence of thermograms showing a cup of tea being made, see images H584/103-106.