Yeah, as previously said, you should put tape or paint on the metallic surface to measure its temperature with your thermal camera.
In my engineering school we did an experiment to measure the emissivity of different type of surfaces .

We could see that without entering the emissivity values, the IR camera would show 64°c for a polished metal plate even if the real temperature (measured with a thermo-couple sticked to the surface) was 74°c .