Actually it's not called a mandau at all if it is Iban, even if concave/convex, but an ilang or parang ilang. 
Some maybe would like to call it a gayang, but based on the "production date" it is probably more correct to just call it an Iban parang (the generic term). 
 
Michael
		 
		
		
		
		
		
		
		
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