> I tried your scene.  It is kind of neat, I am having fun with it.  I see the
> black parts your are talking about, and they are max_trace_level artifacts.
> There are two separate patches that are not rendering correctly.  To
> troubleshoot this scene, I first commented out the HeavyLiquidRegion object to
> work with the alcohol region.  The alcohol region is hovering above the plane,
> presumably to avoid the coincident surfaces issue.  I think the scene is more
> correct when you extend that part below the plane. I changed the AlcoholRegion
> declaration to this:
>
> #declare AlcoholRegion=
> box { <-1.899, -0.2, -1.899>, <1.899, 3, 1.899>
> material { MaterialAlcohol }
>   interior {
>   ior 1.3800
> }
>  }
>
> The -0.2 y value puts the bottom edge below the plane, and the AlcoholRegion now
> renders more correctly.
>
> I did the same thing for the HeavyLiquidRegion  object, changed it to:
> #declare HeavyLiquidRegion=
> box { <-1.899, 2.9999, -1.899>, <1.899, 5, 1.899>
> material { HeavyLiquid }
>  interior {
>     ior 1.4
> }
> }
>
> I also changed the diffuse component and the roughness value from 0 to 1 in both
> of their finishes.  These changes looks more correct to me, as they remove the
> black bars.  I am now adding photons, and it looks pretty cool.
>
> HTH,
> -Reactor

Yeah, it looks much better.  Actually, when I try changing the ior of the heavy
liquid from 1.4 to 1.5 it looks a bit weird again.  This is actually around the
ior I will need I just made a simplified test.  It seems if I turn merge on when
the regions overlap a bit it seems to fix it with even 1.5 ior.  I still however
see what I think are weird shadows of the heavy liquid inside the clear alcohol
region and weird shadows on the top of the heavy liquid box.  I am not too sure
how much I want to play with the diffuse and roughness settings because I am
actually trying to simulate two liquids in a tank and think the settings should
be zero.  They do not seem to change too much anyway.  Some of the extra shadows
are weird though, I wonder where they come from?

-Mike

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