When working on this relatively simple topology, I got some pretty weird shading errors after adding the subsurface modifier (see images).
What is happening here and how to fix it?
Hard to tell, but it appears you have two polygons in the same space.
Not seeing any shading issues, that’s what it should look like with that topology and creases.
[…] why subd at all ??
Because I want the shape to have a smooth curvature. I uploaded the file to inspect.
Pedestal.blend (906.2 KB)
Take a closer look at the weird darkening at the back.
It’s not going to have smooth curvature with those super strong edge creases on every edge
I did not crease the edges that I wanted to have said curvature.
The problem is that the top edge loop gets smoothed inwards by the subdivision modifier, but the hard, creased angle remains in its original position, which causes it to dig into the wall:
In my opinion, this object is not something I would do using subdivision. I would model the object directly from a cylinder with lots of sides (like, at least 128).
But if you must have it done with subdivision, here is how I would fix it: Use the knife tool (k) to carve this shape into the model.
The way I split the polygons keeps everything quads and will react well to subdivision.
Then, push the 2 new vertical edges outward a little bit to make the wall more circular and even, which will fix the shading.
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But there isn’t much to apply any curvation to. There is basically only two edges between other as sharp mark edges… what curvation do you expect ??? I really don’t get where you do want any curve ???
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This is my current workaround, however it disrupts the circular section on the outside.
Have you looked at the blend file I uploaded? I think looking at the model, things will become a lot clearer…
Okidoki has posted screenshots of their Blender viewport with your model open, earlier in this thread 
I’ve also looked at it, and you have too many creases for curvature. There’s nowhere for curves to go
Yes i did and no i do not see what curve you want because almost all edges are marked sharp… there is no curve…
Actually i remodeled it to show the problem…