Wasn't it marabou who wrote:
>hello,
>
>currently I render a scene with an isosurface and a mirror showing that 
>isosurface.
>isosurface is created like:
>difference{
>       object { isosurface1_containedby_box }
>       object { 
>               isosurface2_containedby_box 
>               translate y*-value
>       }
>       rotate x*90
>}
>the result is a nearly planar surface.
>the mirror has reflection 0.8.
>
>but now backside of isosurface is invisible in mirror.
>I heared about keyword <<hollow>>. 
>does it come in play here? if yes, where do I have to place it? what else can I 
>do?

No, it's nothing to do with "hollow". That's something completely
different.

It's more likely to be the fact that you need to specify a sensible
max_trace count, or use all_intersections, in any isosurface that's
involved in CSG operations (like your "difference").

It's also possible, but unlikely, that the max_gradient required for
rays travelling in the reflected direction is greater than that required
in the forward view. Check the "messages" for max_gradient warnings.

-- 
Mike Williams
Gentleman of Leisure

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