"Mike"  wrote in message
<web.4914dde8df3cdb23c6b158600@news.povray.org>:
> I have two transparent objects that I have merged together.  I am a bit
> confused how it is  dealing with the fact that the two objects have
> different refractive indices.  Does it just pick one and if so which one?

As far as I understand how ray-tracing works, we have two effects:

- Refraction is a property of the volume object, but its effect is only
  applied when the ray encounters the boundary of the object.

- The in the merge operation, the internal boundaries just do not exist.

If we consider a light ray that first goes in and then comes out, there are
two points where refraction happens, and each time the effect will depends
on the IOR of the part of the object where the point is.

If the light ray goes in and comes out on the same part of the merge, then
the refraction will behave just as if this part was alone.

If the light ray goes in and comes out on different parts, then the
refraction will happen with different IOR, which is physically impossible.

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