3DVia Composer has a special actor called Cutting Plane, which is normally used to show a section of one or more geometry actors (ie "parts") in more or less the classic engineering look. However, there are some options for the Cutting Plane actor that turn it into a powerful artistic tool.
First and foremost, you can control the opacity of the Cutting Plane actor itself. I nearly always turn the opacity down to 0% for my final view. Once you do this, you can still select the actor from the Collaboration tab, which you'll want to do from time to time to adjust other settings, like...
Front Space Opacity: this is the opacity of the geometry in front of the Cutting Plane actor. It defaults to "0" but I often like to show a little bit of the geometry forward of the cut, as shown below. Note that there is a capacity setting on the Back Space for just the same purpose (which defaults to 255, i.e. opaque).
You can also specify which geometry actors are affected by the Cutting Plane. How? Just pick on the geometry actors you want to be affected first, and *then* activate the Cutting Plane tool. So for example, I want to show a section of a specific part, in the context of a non-sectioned assembly: