First you must get the blade totally degreased and any rust removed .
I have used acetone and then a strong detergent wash followed by a thorough rinse and blow dry with heat .
If you have any hot sun where you are (there ain't any here) leave the kris out in direct hot sunlight for a couple of hours . The most gentle etchants are vinegar or strained Lime juice (lots) ; they are best when used hot ; add a drop of liquid detergent to your etchant so that it does not bead up on the blade surface .
Apply the etchant to the blade with a clean brush or rag quickly covering the entire sword and work the solution around on all the surfaces ; the trick is to keep the liquid moving so that the discoloration of the metal happens evenly .
When and if you see a pattern start to come out keep working and let it darken to the shade that you like then rinse in hot water and wash with baking soda to neutralize the etchant . There may be some tarnish left on the surface so rub the blade down with a soft dry cloth . Finish drying until the blade is warm again with a hair dryer . Spray the blade with WD40 to stabilise the surface ; wipe it clean and apply wax or gun oil .
There are other ways and maybe someone else will offer one . I like this method because it's gentle on the steel .
