Well first of all the obvious...you shouldn't have done that.
Keris rarely have a "cutting edge". It is a stabbing weapon, not a slasher. Sharpen a keris in this way just isn't done.
I think that you might want to try to get a hold of some lab grade arsenic trioxide if you can find it. I think you will get better results. Also, how did you prep the blade before applying the warangan? Did you clean the whole blade back to "white" before proceeding?
I doubt that your keris is all nickel for many reasons, but mostly because you report that it was once black so iron must be present.