We used white oak specifically because it has closed capillaries which do not allow air to leak readily as opposed to red oak, which could leak air readily.
These structures are technically known as tyloses. They're lateral ingrowths of xylem parenchyma (often from the rays) that fill up the conducting vessels over the course of the first growing season after each growth ring is laid down. Tyloses are also why white oak is used for barrels and casks, which are never made from red oak if you want them to hold liquid, and why white oak tends to be more decay resistant than red oak - which is almost certainly the value of tyloses in term of evolution. You will often see old red oak trees with rotten hollow trunks, but white oaks are almost always solid even at hundreds of years old.
Harold, I'm amazed at your craftsmanship. Bravo!