Hey Guys,
Just recently I picked up this sword and I inspected the nakago to find this colouration on both sides, just below the ha-machi area. I complained to the seller who insists that it is not at all a negative feature of the blade, and who in fact says it adds character to the blade.
I've my own thoughts about what this is, but to make this discussion unbiased, I'd like to hear the thoughts of others before sharing my own.
Please also include your thoughts as to whether this would affect the value of the sword.
Here are the photos: