Thanks, Alain.

> Use a difference of the mesh, a slightly scaled down copy of the mesh,
> using a scale statement, and a box or plane.

I do have already an inside vector (<0,0,1>) in my mesh2 declaration. I have
also tried various differences, with the noted results:

// Align clipping box at bottom of cut-off mesh2 surface:
#declare TestBox = box {<0.5,0.5,0.5>, <-0.5,-0.5,-0.5> scale <100,100,0.1>
translate Surface_ClipPlane + <0,0,-0.05>};

// The mesh2, with its bottom clipped off:
#declare test_clipped_surf = object {Committor_50_Volmap clipped_by
{MapBoundsPlane} bounded_by {MapBoundsBoxBig}};

// Texture for all TESTOBJ*
#declare T_TEST = texture { pigment { color rgb <0,0,1>}};

// RESULT: Slab filling just the bottom "opening" of surface:
#declare TESTOBJ = intersection {object {TestBox} object{test_clipped_surf}};

// RESULT: Slab with a hole in middle (inverse of TESTOBJ):
#declare TESTOBJ2 = difference {object {TestBox} object{test_clipped_surf}};

// RESULT: Adds a small ring at bottom edge of cut surface, I guess because
//         the (semi-transparent) surface is duplicated. Attempt to force
//         force the color to opaque dark blue fails (mesh2 has a texture
//         declared in it already).
#declare TESTOBJ3 = object{test_clipped_surf #local T_Committor_50_Surface =
texture { pigment { color rgb <0,0,1>}}; texture {T_Committor_50_Surface}
        clipped_by {TestBox} };

// RESULT: Looks like TESTOBJ2:
#declare TESTOBJ4 = intersection {object {TESTOBJ scale 1.001} object{TESTOBJ
scale 0.999}};
// RESULT: Just wierd edge effects:
#declare TESTOBJ5 = intersection {object {TESTOBJ scale 1.002} object{TESTOBJ2
scale 0.998}};

Am I doing the differencing wrong? Thanks!
Dave

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