Variable IOR is not possible in POV, and probably never will be. It's too
computationally expensive.
You can of course split the object into separate parts and give the parts
different IORs, but that's probably not what you're after.
--
Margus Ramst
Personal e-mail: mar### [at] peakeduee
TAG (Team Assistance Group) e-mail: mar### [at] tagpovrayorg