There are various ways to force a patina--all involve some kind of controlled exposure of an acidic substance to the blade. A lot of people use mustard, vinegar, or you can even use mashed banana or rare roast beef. You can always add more if you want it darker, or you can use Flitz or another similar product to clean it off if you don't like it.
A patina won't "ruin" the Damascus, but it will probably tone it down quite a bit. What you do depends on practicality vs. aesthetics vs. how much trouble any method seems to be.
I think the acid etching looks cool, but I'm not sure if I'd buy a product just to do that.
Kkent2013 wrote:Would you guys suggest to forcing a patina on this knife? Or would that ruin the natural damascus significantly?