Hi Joe, a very very nice Iban mandau! The handle may not be very 'fancy' with faces and everything but the whole sword n scabbard are very old -I would estimate 1870 maybe even older.
Seen the leeches pattern on the scabbard it originates from the Iban dayak of Sarawak (Malaysian part of Borneo) and those many smaller brass points inset in the blade near the handle I have seen in many swords originating in an area closer to Sabah; Murut-tribe.
Therefore I would bet my money this mandau comes from the Baramriver-area Iban Dajak.
Love the scabbard, n nice piece of twirly carved deerhorn on side, openworked blade . . . .AAAHH!
If the sword was mine I would just put some woodglue (watered down perhaps) on the brittle resinpart of the handle and respectfully clean the blade (remove rust). Oh and brush off the dust . . .but am sure you done that already
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Good luck n enjoy