Re: Finishing question, mainly re tung oil
Lyn J. Mangiameli
>The shine of any finish will depend principally on one thing: how coherently the light is reflected from the finish(s). The opposite of this is that light is scattered off in different directions. For (fairly) clear wood finishes, the amount of scatter is going to be determined by three things: The smoothness of the underlying wood surface, the clarity of the finish itself (i.e., does it contain particle inclusions--which are sometimes added deliberately to achieve "low gloss" finishes), and the smoothness of the external surface.
Thus a woodworker can control shine or gloss by:
1. Choosing how finely they will sand the raw wood
2. Choosing a finish that has or doesn't have particle light dispersants
3. Controling how evenly the finish is applied and choosing a finish for its surface characterists when dry.
4. Choosing how finely they will sand or buff the final finish. ("Rubbing out", is more than leveling a finishes surface, but is the way flat woodworkers select the amount and uniformity of light dispersal by the depth and uniformity of the final scratches left on the surface).
Sometimes one factor will predominate, such as having particle dispersants in the finish will dominate over how finely the wood surface is sanded, but generally all factors do not have to be optimal to still achieve a shiny finish.
Bringing this to the original question Tung oil is a drying finish that shrinks slightly as it dries. This shrinkage causes micro ripples in its surface, that lend themselves to a more "tactile" feel and greater light dispersal. In some circumstancs this is desirable. When it isn't, sanding or buffing (which basically both come down to controlled abrasion) will level the ripples and increase the shine. Buffing with wax will also allow the wax to fill in the areas between the micro-ripples and achieve a smoother outer finish which again will contribute to more coherent light reflection.
Polymerized tung oils shrink less (as do products that contain lesser amounts of tung oil because other finish components, such as resins, are mixed in) than pure tung oil, thus having lower amplitude ripples from drying. I almost always prefer Polymerized Tung Oil (I use the Lee Valley products) to pure tung oil, but sometimes the latter is preferable specifically because it has the softer (both light and tactile) characteristics that result from the micro-ripples.
