How do you raise the grain of a walnut?
Consequently, how do you raise the grain?
Pre raising the grain with plain water and lightly sanding with ~320 grit to remove the raised grain (after drying) will allow a WB stain to be applied and have a smooth surface after drying to top coat. If no stain or dye is used, then there is really no advantage to pre grain raising for a WB topcoat.
Similarly, what is the best finish for walnut? Lacquer
Thereof, is Walnut open or closed grain?
Precise definitions of open and closed grained species don't exist, but softwoods are generally considered open grain, as is oak, ash, mahogany and walnut. Closed grain species include maple, birch, cherry and hickory.
How do you smooth the final coat of polyurethane?
Apply only one thin coat. Then, remove any dust nibs with 1,500-grit sandpaper or a piece of brown paper bag. Finally, using a soft cotton rag or polishing pad, buff the finish to a high shine using automotive paste wax, photo below, which has fine abrasives that polish the finish even further.