You made no mistake.  This is what appears to be a previously undiscovered bug
in POV-Ray.  I found the problem in POV's code: POV-Ray depends on a few global
texture and weight lists for multi-textured objects like blobs.  Unfortunately,
when it computes textures during shadow testing, it forgets to push the values
onto a stack and subsequently mangles the list.

Therefore, your temporary fix is to add the "no_shadow" keyword to the "merge"
object that the blob is in.  This will cause POV to skip the shadow test and
protect your blob's texture and weight lists.

   merge { 
      sphere { 
         <-0.5, 0., 0.> 
         C_VDW_Radius 
      } 
      sphere { 
         <0.5, 0., 0.> 
         C_VDW_Radius 
      } 
      texture { _T_VDW } 
      hollow 
      no_shadow // this will fix your problem
   } 

I'll tell the POV team about the bug and also how to fix it.

-Nathan Kopp

Siegmar Kardinal wrote:
> 
> hi,
> 
> when I put a blob inside a hollow glass object the colours of the
> blob parts are no longer smoothly changed but switched somewhere
> in the middle. the following input lines and the jpeg image (so they
> are properly attached) show the effect by
> comparing a blob inside and outside the glas object.
> 
> Do I make a mistake here?

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