Thank You Ferdinand,
This Problem is not mission critical here, but it kept coming at me (at night). Anyway this is hopefully useful for others in some way, as its to complex for very little gain in my case ... I can fake a similar material with Fresnel colors and some falloff / or even thin film hacks.
If anybody wonders, the Scan (gradient) is from an X-Rite Material Scanner (TAC) which normally has a proprietary file format.
Thank you for your time regardless.
mogh