As other posters have noted, both hydrochloric acid (HCl)and ferric chloride (FeCl3)will work. HCl is also known as
"muriatic acid" and is sold in swimming pool supply stores, Home Depot, etc to adjust the acidity of pool water.
FeCl3 is sold by electronics hobby suppliers as a 'PC Board' etch.
Be CAREFUL with both these, they are both corrosive and will burn skin, eat holes in clothes and have nasty fumes
that will eat your lungs and eyes and corrode metal items that are stored in the same room.
When used to etch steel/iron they provide "grain relief", that is, they will show the boundaries of the
metallic grain structures on the metal surface.
They will NOT make a plain blade appear to be Damascus. After acid etch and a few other magical treatments
they can give an 'antique' finish like the one seen here:
http://www.agrussell.com/knives/by_...wrangler_large_bowie_with_beaded_sheath_.html
BUT don't expect to fool experts with a synthetic antique finish; a close analysis of the blade surface patina
can easily differentiate between a real antique and a chemical look-alike.
Also, the acid WON't etch nor penetrate to .5mm unless you leave it to soak a LONG time. The problem is that you
should mask off the blade areas you don't want etched ( black vinyl electrical tape will probably work),
but most masks will fail by the time the etch reaches .5mm.
Bottom line is: you'll need to take strict safety precautions, experiment with masks, soak times, etc before you
risk a valuable blade.
Last word: do all this OUTSIDE...one whiff of HCl fumes and you'll know why...after the coughing fit has subsided.
JMH
