Toast. Thermogram of toasted bread in an electric toaster. The colour-coding shows variations in temperature. The scale runs from white (warmest), through red, yellow and green to blue (coldest). Thermography records the temperature of surfaces by detecting long-wavelength infrared radiation. The heat of the toast contrasts with the cold of the casing of the toaster that insulates and retains the heat of the heating coils. A glow at bottom centre reveals a gap in this insulation. The top edges of the toast slices are colder than the side areas. This is because the coils heat the bread from the side.