The “Metals” page at the Far Associates website, states :

tungsten1“The emissivity of metals often changes with wavelength. This means it is very difficult to determine what emissivity should be entered in passive, traditional pyrometers (all those that do not determine the emissivity during measurement). An example or two will show the difficulty.”

The graphs shown are from the “Thermophysical Properties of Matter ” vol 7; Thermal Radiative Properties, Ed By Y.S. Touloukian and D.P Dewitt, IFI-Plenum, New York 1970.

The original graphs in that volume were accompanied by the data represented by each curve, the literature citation for each and a description of the measurement and sample details represented by each curve.