I'm with Gene - no need to soak a Arab/Persian/Indian blade for etching: This just increases the risk of corroding the surface which should stay smooth.
If it is a wootz blade, treatment need to be specialized and usually very short (seconds).
If it is a pattern-welded blade, swift wiping with ferric chloride will bring out the pattern (retry several times if the contrast or pattern doesn't show nicely). If it looks too bold, try wiping with hot vinegar after a quick repolish (by hand - no power tools!).
Regards,
Kai
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