Most default surfaces from ArchiCAD18 and later have caustic channel on by default, so unless you made stuff from scratch or are using an ArchiCAD17 or earlier project, it should work out of the box so to speak.
The image I show, has mostly 'white paint' as surface. Which is the one I checked before the render.
I don't generally go into these fancy render settings, go for a more sketchy look, so you've reached the pinnacle of my knowledge here, I'm afraid
Erwin Edel, Project Lead, Leloup Architecten
www.leloup.nlArchiCAD 9-26NED FULL
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