The Render Blog posts a great article in creating your own custom fresnel curves in Maya.
A few years ago we would use the facing ratio and a ramp to achieve that effect
The fresnel response can suggest a wide variety of different materials, and João does a little experiment analyzing the reflection curves from a test scene render in Maya to find some values.
João walks you through using Maya nodes to draw the fresnel curve manually in Maya, and writes a python script that can assist in drawing the curves using fresnel formulas found online.
This is quite a bit more technical than using the old and nonphysical method of using a ramp and a sampler info node to get simulated fresnel effects in rendering. Have a look at the Redner Blogs’ post for Custom Fresnel curves in Maya here.
