Toast. Thermogram of toasted bread in an electric toaster and butter being spread on a slice of toast. 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. The butter (blue) is also cold, as it would have been stored in a refrigerator. Heat reflections are seen in the reflective surface of the toaster.