Hello Pusaka, A few years back there was what looked to be a rencong with a copper blade listed on epray. I almost bid on it as I have a small collection of Philippine daggers with copper and brass blades, but in the end either decided not to or found something more in my personal field of collecting to spend my money on. I have also heard that these were used to protect their owners from magic from those who wish to do them harm. I have also been told that if one of these were actually used on another person that they were supposed to produce a wound that would not heal and eventually lead to the demise of the person stabbed with one. I even have one example where the blade has been coated with silver arsenic which I assume was to help in hastening that process. Here is a link to some photos of these items.
http://www.vikingsword.com/vb/showthread.php?t=20787 As for cutting and strength, copper bladed weapons and tools were used for hundreds if not thousands of years before the discovery of brass and bronze. Copper tools were used in the construction of the pyramids and the tombs of many ancient peoples and civilizations.
Best,
Robert
Best,
Robert