I have been having fun with using black tempera and black ink on my paintings.
Tempera you need to cover with a coat of clear medium, because it is watersoluble, and therefore, not very archival. I would not want to risk it. But the good news is you can wipe it off with water if you don't like what you've done, and start again. The black ink, you do not have to cover with clear medium if you don't want to. I was afraid to put it on, fearing I would make a mistake and could not remove it, until I found out you can remove it with rubbing alcohol! That really freed me up to have fun and experiment. So, try it!