measureing tool for measureing oil and fat remains on steel surface

[jangolobow]

Hay I am searching a measuremnt tool for measuremnt of oil and fat remains on steelsurface (all type cast forged, stainless steel etc) prior painting it. i would need a small sensor portable) if exist. some ideeas?
thanks

 

[Compositepro]

It can be as simple as a "water break test" or an infrared spectrometer. You can Google those terms.

 

[btrueblood]

Or a uv light.