I have a mesh which I have imported from an OBJ file. I would like to apply Material A to the section of the mesh which is on one side of a given plane, and apply Material B to the section of the mesh which is on the other side of that plane. A potential plane is indicated here as a blue line. Note that it does not necessarily intersect the centre.
To do this, I need to split the any faces which intersect this plane, and select all faces on one side of the plane so that I can apply a material to them. How can I do this in the current versions of Blender?
I've tried using the K knife tool in Z cut-through mode, but the cuts haven't been reliable. Even when they were, after the cut was finished I couldn't figure out how to select only the faces on one side of the cut. (The details were too fine to be reliably selected with any tools I know, such as the C circle select tool.) I tried using the B selection tool, but it only selected the faces on the near-side of the mesh.
We used to have a procedure to cut a mesh using a plane in Blender 2.4, but it involved using mesh boolean tools which appear to have been replaced, and I can't figure out how to adapt it.