Unwanted transparency

I created a solid by extruding planar curves. The extrusion went fine. I checked the rather complicated solid and I even got a volume number. So the solid must be ok. Nevertheless, the top and bottom suface remained transparent. Can anybody help? Thank you!

Without seeing the file it’s hard to say but it sounds like a bad edge on the srfs in question. Try Explode followed by RebuildEdges and then Join. I’m assuming the transparency is a render mesh issue caused by a self intersection.

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Thank you Brian for your swift reply. I followed your steps. Regrettably, it did not lead to the required result. Quite the contrary, the solid was no longer ‘watertight’ thereafter. Maybe I should tell you how I often work. I import relatively complex outlines from Illustrator. I know, these outlines may cause problems. That is why before importing I run them through scripts that will eliminate overlapping anchors. (If you know the best scripts for importing illustrator files into Rhino please inform me).You are right, sometimes I get a prompt with the extrusion command that there are self intersecting parts. (while there are not, but apparently Rhino sees them. I can’t). Most of the time this does not affect the extrusion. But now the mysterious part: when I use the watertight model (with only horizontal transparent parts, the vertical parts are visible) for further transforming commands, often the transparency disappears (not always). Another remedy I use is saving the model as a stl file. That also can take the transparency away. Do you have any clue what is going on, and which procedure is best to follow? Thanks.

Hello - please post a 3dm file with the input curve and the resulting extrusion, or send to tech@mcneel.com.