Some ideas about the reworked Corona Physical material:
With the addition of the Complex IOR, Corona finally has lost its innocence (sounds a bit less conspicuous than "virginity" ;)).
Corona was always meant to have the simplest GUI (material and render settings), and I truly believe it lived up to that promise - and it still does.
Getting more (advanced) features is a good thing and losing one's innocence is part of growing up. But I think now it's also time to consider adding more features that MIGHT clutter the interface, yet add to the value of the app, like Nested Dielectrics or a shading modes menu (with GGX, Blinn, Ward and whatever else). The first deed is done, don't stop there ;)
Back to the matter at hand, the Complex IOR and metals.
It's a bit lost back there in the Advanced tab, I think it should go in the Base layer with the Edge color. It were nice if, with radio buttons, we could choose between "Edge Color" and "Complex IOR", preferably the now not needed GUI elements would collapse/be hidden.
Of course, the presets in "General" would now have to apply either the correct edge color settings or the proper "Complex IOR" settings, because I doubt people know such settings by heart (especially the Complex IOR settings).
Leaving the Complex IOR settings in Advanced is a bad idea (in my humble option only) because activating them means "lights out" for half o the Base layer settings - confusing. If you get such material and have no idea there's a complex IOR hidden somewhere, you might be scared and go back to Standard render (what an awful thought!).
On the other hand, if we create a pure Dielectric material, "Edge Color" could collapse/be hidden. It would mean a further return to the good old Corona Render philosophy of a clearly readable GUI.
Now to an issue I'd actually call a bug. Create a new Physical material and apply a "Copper rough" preset. Go to advanced and enable Complex IOR (and now you see why it should be in Base layer and linked to the presets) and your copper turns golden.
Now apply a glass preset. All is fine, the Complex IOR is inactive. And finally apply a Chrome preset. Yellow chrome, nice! And all because somewhere deeply hidden the Complex IOR is still active. The preset should handle this "somehow".
Another issue:
I think it were be better if applying a preset would clear the texture slot of the metalness setting.
Thanks for listening,
Michael