Your post about a blacked out background is now clearer. You are trying to increase the contrast only, so the selenium (or other) intensification may work. For an extreme possibility try contact printing a paper-print on to another sheet of paper, then contacting that again to get your final result. It is also possible to adjust density on the back of the paper "interneg" with pencil, or paint etc, in order to mask the result when it is contacted again. This sort of approach might achieve what you want.