Bill Moran
http://en.wikipedia.org/wiki/William_F._Moran
used hydrochloric acid, as I did myself until I discovered ferric chloride.
In fact, dilute hydrochloric acid , and virtually any other acid, if handled correctly, will give a more realistic and subdued stain than ferric chloride.
If you need a topographic etch before you stain, hydrochloric acid is probably better for this, but in my opinion the nicest finish to damascus is a very light etch that leaves you with a smooth polished surface and a subdued stain, rather than the in-your-face high contrast that most knife show buyers seem to prefer.