This video shows some options for compositing and for illustrating using Cinema 4D alpha channels. One of the handiest tricks as an illustrator is to render different versions of a scene and by moving the time slider and rendering again. This creates multiple version of the same scene that you can composite in Photoshop, the frame name changes so they don’t overwrite each other.

For example, render a rusted version of your type, move the time slider 1 frame and re-render with a glossy texture. Both need alpha channels. In Photoshop, use the alpha to select the objects from the first scene and then shift-drag the selection to your other scene. Magically, the object is placed pixel-perfect on top of the other one in the same location. You could then use a Layer Mask and sponge brush to ‘reveal’ the version under for a rusted, glossy paint look.