I am trying to design a heat source for use with testing the functionality of an infrared thermometer. I am happy with my circuit, I have a surface heated to a nice, constant 50°C (as constantly monitored by a thermocouple).
The surface is just an aluminium alloy, which I have sprayed with a matt black paint. Unfortunately, finding the exact emissivity of the surface is proving difficult. I am unsure whether to keep this as my surface, or find something else. The matt black paint is supposed to have an emissivity of 0.93-0.97, yet aluminium alloy has a very low emissivity.
A table can be found HERE which shows the emissivity of different surfaces.
Thermal conductivity of different materials can be found HERE.
The reason I chose aluminium was because it is easy to get hold of, it is not expensive and has good thermal conductivity. Because of its low emissivity though, I had to paint the surface in order to test the infrared thermometers.
I did a lot of research on the subject and there are so many places that specify using a black surface to get the best emissivity (as in closer to 1.0), yet there are some black surfaces which have a very poor emissivity as seen HERE. That document also shows some white surfaces as having good emissivity, and white is the furthest from black you can get!
There are other articles such as this one HERE that look at the effect of the smoothness of a surface, which I found interesting as some materials with smooth surfaces have a good emissivity, even if not black.
So my question is: What is more important when it comes to emissivity (getting closer to 1.0), colour or surface finish? Do different colours or surface finishes affect the wavelength of the thermal radiation? If so, why and how do these factors have an effect?