Thank you for the elaborate explanation, Boedhi Adhitya.
I counted the luk on the old blade in the way you described, and I ended with 12 luk (at my index finger). So you are probably right in stating that the blade used to have 13 luk.
Alam Shah, I appreciate your comment on my kerises, but I wonder why you are so negative about the old keris blade. True, it's not in perfect condition. But I feel that this old blade still has something. I don't know what attracted me to it.
By repeatly washing the blade, it's a natural process that the blade becomes thin and starts losing some 'ricikan', don't you think so ? People in Indonesia, cherish their old family kerises. I've seen pictures of kerises in the same condition, which were and are respected for their age.