I am working on a toilet paper holder that is recessed into the wall. How do I add a wall mask (I am assuming that is what is needed) so that the wall does not show on the object? What object would I clone to make this? If I used a window the light would not be a good thing. Is this something that can even be done? Thank you for your help.....Cat

Ohh it can be done, I've seen a fireplace flush with the wall and a bookcase recessed into the wall.
I don't know how those people did it, but I assume they used a window wall mask.
Why not try it with the smallest window there is and make the wall mask to fit your object and see what happends?
I'm sorry I can't help you with this, I've never done it before, but I know it can be done.
If you've problems with light coming through, maybe someone here will know how to fix that.