How do you control IOR with a map?

[pailhead]

I'm thinking how to achieve, seeing as it can go from 0 to 100, it leaves very little steps if b-w map is used between these two values?

[pokoy]

You can achieve that using a composite map. You can either stack several maps in the composite map while setting their layer opacity to a specific values (for example one map with 1,6 and another one with 2,2 and so on) and masking them with opacity maps. This can be quite complicated if you want to have many different IORs.

Another way is using the standard max falloff map, set it to the highest desired IOR (for example 1,6) and put a b/w map in the side slot of the falloff. This way the map's whites will produce an IOR of 1,6 and everything below will be scaled accordingly.