you could use the link below for solution....i think like steel it would work with anything i have used salt water on steel the proper solution might give you a better etch but a lot of things could be used...
there are a few options out there for titanium the link below is just one.
also i would think both 6-4 and CP would work pretty much the same
http://usaknifemaker.com/knife-makin...multi-use.html