IOR problems

Hi. Sometimes i got a problem with IOR. I don’t know what’s wrong, but when i use IOR and set value > 1 then become some grey part on the texture. The only way to fix it is to set value of IOR to 1.0. How to fix the problem?

There’s no problem to be fixed. IOR below 1 means that the light is travelling from a slow medium to a faster 1 (i.e, from inside water to air). This is also what happens automatically when the face is hitted from the backside (i.e, inverted normals).

The gray you’re seeing is just the total internal reflection.

Thank you. I just Flip Normals and all become great)