Thank you both, Rick and Jens
Jens, yes is black lacquer.
I have found this on the mr. Yarom's site:
"Scarf welding was done by welding two ingots of steel in or around the upper third part of the blade, in order to provide the blade with both strength and flexibility. It was a common technique since many centuries and found on both Indian and European quality swords. Here the welding point is clearly seen in the close ups as a darker semicircle."
I think that this could be the case also on my blade.