What is the effect of scale on the surface of steel, when measuring temperature with an infrared thermometer?

If the scale is tightly bonded to the steel it will usually have no effect because it is the same temperature as the hot target. However, if the scale breaks loose it will cool and cause a cold spot on the target. If the instrument is a single wavelength instrument it will indicate a low temperature. If the instrument is a two color and only a portion of the spot is filled with the cold scale it usually will not affect the temperature indication.