Poisoned keris blade

[oracle_2010]

Hello, greetings everyone!

I am new to this forum, wishing to learn more about keris.
A few months ago, I got this one keris originated from Pagaralam, South Sumatera.

When I received it, the sor soran part partially covered in rust, so I decided to soak it in coconut water to remove the rust. After a few hours, I took it out and clean it with lime juice. Then I notice something peculiar.. the lime juice that dripped from above the sor soran to the pointed tip is changed to black color, almost look like the ink from a squid.

Indeed there is noticeable difference in the blade itself, from the base of the ganja to above the sor soran, it is plain grey. But there is pattern like striped black and grey ribbon from above the sor soran to the middle of the blade length. Then from the middle to tip, it is colored almost completely black.

A keris expert told me that it is actually a poisoned blade.
Is there really such keris? If so, how dangerous is the poison and how is it made? Because opinion has been varied from wether the way iron is forged which created poisonous blade or certain poison from another source was added in the making of the blade. I would also like to get opinion about the tangguh of this keris.

Attached, I send you some picture of the keris.