The file work here looks like the
ron dah on Indonesian keris. It is interesting to see how the "open" form of the
ron dah developed on this blade. If we look at the examples towards the spine of the blade, they are "closed" at the top. But as we progress towards the tip they become more "open." This must surely be due to greater corrosion towards the tip, resulting in loss of the thinner areas that enclose the space.
Alan Maisey has commented on a similar phenomenon occurring on a decorative piece of metalwork he acquired. He thought that the "closed" form may have represented the Hindu "om" while the corroded form ended up looking like
ron dah.