Shame on you for posting such nice images in such a small size.
You make me want to see much larger images!
It will be well worth your time to get rid of the halos that you mentioned in the last one.
In the first one, notice that the shell itself (as opposed to the hole in the middle) has less contrast than the image of the same shell in the last one. I like the additional contrast. Also notice in the first one, the shadow helps define the object. If you want to have more of an abstract look (you may not), you could eliminate the shadow either by how you light the subject or how you post-process the image.