hi
are you acid etching: as in applying an asphaltum resist, cutting a pattern into the resist, and then using the acid to erode the base metal ? ( such as many designs were put into knives, way back when )
or... you have a knife made of patternwelded steel and want to show the contrast between the two metals ? if so ...it would be good to know what base metals make up the damascus composite
eg... if it was 15n20 and 1095, then ferric chloride would be a great choice
or if it is the same metal folded upon itself ... maybe a heated lemon solution may work, pending on how you've polished the piece
or even dilute nitric acid and distilled water, which works well for many alloys and also for revealing banding, and hamon ( not an acid for a novice, as the reagent grade stuff is quite strong )
or.. acetic acid vinegar will work if given enough time ... but results are not what i'd call " eye candy "
also, becareful to neutralize and wash down the blade with water after the ferric dip... the Cl has a habit of corroding later on if its not delt with...