Thank you for your comments.
I apologize for my late response but lost my password.
I don't think this Keris Sajen is very old (XXth entury but before 1970) but even if it doesn't respect the standards I think it was created for a local spiritual use because it does not seem to have been made to look like a very old antiquity and is very different from the mini keris for tourists I've seen.
The photos were taken after a first cleaning, the remaining rust is really very resistant. I hesitate to use the pneumatic micropercutor of the museum where I work because I am afraid to mark the blade.