Sherwin Williams Ultra deep tint base(A100), but do not add any color. It is paint that dries clear(as long as no color is added). It is milky white when applied, then dries transparent.

The following picture is a close up of a walnut cross I built and has been installed over a year now, full sun/wind/rain/snow. I applied two coats of the A100 in August, 2014(was stored inside) and installed the cross in place in March, 2015.

HandyMac that wood looks beautiful. The finish looks (and sounds) very much like a matte acrylic varnish I used to use from Pratt & Lambert. For this application, though, I don't want something that sits on the surface but rather a good penetrating sealer or oil or ??? something. Thanks for the suggestion and for sharing your picture.

Still looking for suggestions but may also try cross posting in Building a Home

The finish is paint. Paint resists weathering(the gray color that happens) because of the titanium dioxide it contains. That is why paint is the longest lasting finish for exterior use.

That paint will last much longer than any sealer/penetrating finish on the market, without annual or so upkeep.