Reflections behave following the Fresnel law. Generally reflective materials exhibit more reflection approaching a viewing angle of 90°. This is why Schlick implemented the ‘Schlick trick’. That is. You control reflection slope based on 3 simple parameters: reflection at 0°, reflections at 90° and the slope between the two. This gives a reasonable fast and intuitive way to model reflections. In facts with Fresnel alone is difficult to catch metal reflections. You have to set a very high IOR factor to model metals and this not so intuitive.
The IOR parameter once enabled ‘UseIOR’ in the reflection rollout, remains in the Refraction rollout. This is like that because you better use IOR for glasses and complexIOR for anything else.
On the other side the 0/90° trick does not come with a database of settings to model various materials, so generally one just tweaks reflections until they look good.
Because of this we added Complex IOR which is well documented and comes with a database to model different materials. For example one can go here: http://refractiveindex.info, and simply write down N and K for the three main RGB wavelengths and input them directly in the material Advanced rollout ComplerIOR section (eventually Red is at 700nm, Green at 550 and Blue at 450nm). Or simply choose an available preset.
Results are very good and consistent. Just take a preset, set reflection weight and tweak glossiness to resemble the metal you’re trying to model.
They have all been shaded with just a couple of clicks.