Amazing piece….. WOW. I have built some outdoor projects for clients before and I always run into problem in which can't make there mind up on the finish. There's only too that I have used. One is tunn oil, and POLY.
I really don't like Tune oil for outdoor, because you have to maintain it all the time, and must clients I have built outdoor projects don't like too. I like the Poly because it last a long time, and it keeps the water from entering the wood, but it makes for a more shine piece , and in the garden most people like a more dull finish. That piece you have should be in a gallery…
You can try a wood seller, a poly sand seller, but make sure the finish has an oil in it, or the piece will try out with the sun.
Hope I could Help.
Thanks, Michael Frey
Portland, OR
FREY WOODWORKING INC.