I read somewhere it's impurities in the copper. Thats about the woodiest i've ever seen badthad. I have a couple decent ones but no good photos. They're hard to photo,I haven't been able to get any pics that show any detail.
I would not think so, but I have seen some that it might be. There was one posted here about a year or 1 1/2 ago (1925-??) that was absolutely gorgeous.