It looks like weathered wood to me, like the base of a very old and weathered tree trunk, or a massive limb perhaps. Regardless, it seems a bit dark to fully appreciate those repeating,undulating lines. It just seems a bit too...dark...to FULLY appreciate what's in there.
Wow, quite splendid indeed, the fluency of those lines are very swift, I can see why it caught your attention.
These are one of those pics that you could hand in an art gallery, nicely framed, on a huge print.
My cc, I don't know why, but it feels that it looks better If it was turned Landscape ways, then it looks abit like a mountain range