cottonwood

Look up Peter Bloch, "Bloch of Wood" over in New Hampshire - he does translucent lampshades from popple/cottonwood/aspen (the curse of common names, but anyway). However, of you have alread split all the logs lengthwise you won't be able to replicate those (he just hollows the pith right out, and the ring that's left dries nicely).

as well as creating a lot of ash and sometimes stinks while burning.

I'm in the process of rough turning the large collection of chuncks I've collected including the cottonwood. Over the weekend I turned part of the second log. It was highly figured with lots of contrasting colors. I rough turned a 14 inch bowl then took a cut off from rounding the blank and turned it also.

I kept my chisels sharp and It turned like a dream with n> I'm always on the prowl for free wood.

Yep, as long as you cut instead of trying to bully it, it's nice. Be advised, though, that it will be a bit weak once you dry it. A steady is a real good idea at 1/4 or so thickness. Plan on taking at least one piece down below 1/4 and oil soaking it so the sunlight shines through.

Leaving it at about 1/2 or so on the bottom, tapering up, and treating with walnut oil makes a great popcorn bowl. Thicker bottom with lots of air doesn't transfer heat to the lap, and the walnut oil won't blister from the heat of the unpopped kernels.

As in translucency? Any curing oil, though price would dictate linseed or tung. I'm partial to linseed - boiled, of course - because I don't care for the scent of tung or the slight haze it has in surface finishes. Finish with any linseed-based varnish for a film finish and additional "depth."

Be sure to allow time to cure, because it will take time to get oxygen cross-links inside the wood.