Hi,

When a ray first enters an object of, say ior 1.5, and then one with ior 
1.3 (without leaving the first object), is that IOR than regarded 
relative to the containing object, or absolute?
And, when the ray than leaves the second object, does it "remember" that 
the outside has ior 1.5?

The reason I ask is, I made a glass with a liqid inside.
The common way to do this, is to scale the "liquid" by, .999.
But this causes the render to become very slow, because of reflections 
between the liqid and the glass, because there are now two surfaces where 
in reality there should be only one. So I had the idea to clip the glass 
by a slightly bigger inverted copy of the liqid. 

This is much faster, but I'm not sure if it gives correct results?

Lutz-Peter

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