Thanks for confirming. Is it possible for you to send us your file? So we can test and troubleshoot it on our end. You may send it to support@d5techs.com and have it titled “Clov-Forum Black Border from Material Selection appear”
Thanks for providing your file. After testing, I’ve determined that the outlines are a result of the wall’s material colour being visible in the crevices where the panels are placed. Due to the small gaps, the underlying surface is showing through.
Black Material Colour assigned behind the wood panel or other surfaces.
Note: Because these gaps are three-dimensional, they are factored into the light calculations. This results in shadows that emphasize the gaps, creating the visual effect of an outline.
This is the original render where i have spoted the issue. Please look where the water meets the stone. You can see the black line outlining the stone material.
In detail, you can see the black line following the contour of the stone material
Because these gaps are three-dimensional, they are factored into the light calculations. This results in shadows that emphasize the gaps, creating the visual effect of an outline. Also, path tracing also plays a factor in making these gaps darker. I made some test in your file.
Path Tracing is DISABLED and the Color of the wall behind the stone is set to WHITE instead of Black
There is a huge difference when PT is disabled and the material colour of the wall behind these Stone/Wood Panels is set to white. It is also important to know that when path tracing is enabled, dark areas appear significantly darker due to its more accurate simulation of light behaviour.
If you wish to eliminate the outline effect that was produced because of these gaps, I recommend following the first 2 images and their settings.