If you have had the chance to see Roy Underhill live more than once, it is likely you have seen his red oak demonstration. Roy’s demonstration is to take a chunk of red oak, submerge one end in water and blow in the other end. (End grain to end grain.) The water bubbles with Roy’s exhaled breath. He then attempts the same with a piece of white oak producing only a red face and no bubbles. Air (technically a fluid) moves freely though the red but not the white oak.
Red oak is a ring-porous wood with large pores (vessels, xylem) located between the growth rings. In red oak these pores are continuous and open like straws permitting unencumbered movement of fluids. White oak has membranes in the pores that block, to a large extent, the movement of fluids.
It is Toys for Tots time again locally under the auspices of Fred Ford and the Triangle Woodworkers Association. This is my second year hosting a workshop and building toys. I am again building the bulldozer with animated blade:
Last year I was given only white oak for the build. This year I took both red and white. The wood is a donation and is typically shorts from The Hardwood Store of North Carolina and others.
After forming the body, the next step is to start adding the decorations, the exhaust stack and headlights (not shown). To avoid a choking hazard (and subsequent lawsuit), I wanted to make sure everything is well glued in a properly sized hole. A tight fit.
As I tapped home a 5/32″ axle, I saw a small spot of glue on the front of the body. My first thought I was careless with the glue syringe.
I cleaned it off and moved on. When I saw the second spot, it occurred to me what was going on. The axle is a piston fit and the excess glue is being squeezed out through the large, open pores.
This did not happen in the white oak bodies.
There is a reason wine barrels are made from white oak and not red. And boats, not red oak. It is good to keep fluids where they belong. Or at least where we believe they belong.
Science in action.
If you are a wood nerd, here are two more links that might be of interest. The first is a video demonstration by shipwright Louis Sauzedde of fluids and oaks.
The second is a page of images of various ring-porous domestic hardwoods.