Yes, this gun blueing stuff is also some kind of acid mix, dont know what exactly. Perhaps the manufacturers are not so keen to tell - because then you wouldn't have to buy their products anymore. :)
The etching of damascus can be done with car battery acid, I've seen that in videos. Not pure acid! It only takes a few minutes. Without that, you will hardly see a difference in the steel layers - they just all look silvery, like steel does. Sure you can find plenty of "how to" videos on YT about that.