Note: this article only applies to the old Corona Legacy Material. Fresnel reflections are realistic, so they cannot be disabled in the new Corona Physical Material.
There is no way to completely disable Fresnel IOR for Corona materials but setting its value to 999 will make the object almost uniformly reflective.
Examples
1. Fresnel IOR = 1.1
No diffuse color (pure black):
With diffuse color:
2. Fresnel IOR = 1.52 (default value)
No diffuse color (pure black):
With diffuse color:
3. Fresnel IOR = 6
No diffuse color (pure black):
With diffuse color:
4. Fresnel IOR = 32
No diffuse color (pure black):
With diffuse color:
5. Fresnel IOR = 999 (virtually uniform reflection level)
No diffuse color (pure black):
With diffuse color:
Scanned skull model was kindly provided by Ten24 3d Scan Store.
http://www.3dscanstore.com/
Note: this article only applies to the old Corona Legacy Material. Fresnel reflections are realistic, so they cannot be disabled in the new Corona Physical Material.