rim edges

[moonkoral]

How to make the edges of the rim like in the attached photo (I mean rounded edges, like 3D)?

[PixLab]

You need to make a map

Example starting with a circle:
Before to start your ring layer need to be at the image size > Very important, to be sure got to Layer > Layer to image size

   

Select the layer of your circle in the layer stack/dialog, right click on it and select Alpha to selection, or make a selection circle and go to Select > Border... to make your ring, fill with a color.

Then create a new layer, still the selection active > inside the selection put a black and white gradient with those parameters

   

Once it's done, Select > None, then blur that gradient layer

   

Once it's done, untick the visibility of that layer map (don't delete, just make it non visible)
Then Select the layer with the flat ring in the layer stack, and go to Filters > Map > Bump map..

See settings (click on that button in the bump map window to open a dialog and input the map you've created)

   

[moonkoral]