Wood Finishing Overview (by Mike Melofchik)

[mlcswo]

The application of colors to wood surfaces often wreaks havoc on the finished piece that the average woodworker has spent hours designing and building. Many woodworkers think the application of color to a wood surface is opening up a can of hardware store purchased brown liquid that smells bad and ends up showing off all the imperfections of the wood. Fortunately it doesn’t have to be that way. With a few simple techniques, you can be well on your way to a top quality finish.

This month, I would like to begin by discussing how to control the depth of color penetration on end grain versus side grain and hopefully shed some light on how the wood behaves as a material. But before we begin, we first need a basic understanding of tree growth and wood technology.
Trees grow from top to bottom as well as from inside to outside. At the very center of the tree is the pith. Next to the pith is the harder, and older heartwood. Further out towards the bark is the softer and younger sapwood. Separating the sapwood and the bark is a very fine layer of cells called the cambium layer. On some species such as cherry and pine, there is a very large contrast in color between heartwood and sapwood. Other species do not have such a dramatic color contrast. Whether there is a striking color contrast or not, the functional properties of heartwood and sapwood are identical. The sapwood has the primary function of transferring nutrients and water throughout the tree. Its living prosenchyma cells conduct sap for the tree to use, and the parancyma cells store minerals in the sapwood. In heartwood, both the prosenchyma and parancyma cells no longer function.

To make sense of the biological aspects, consider a tree as a cylinder. If it is cut into slices lengthwise, the length of the board consists of side grain, running perpendicular to the growth rings of the tree. These flat pieces can be visualized as a box of drinking straws.

The drinking straw analogy is a useful starting point to describe how wood (the tree) absorbs liquids. When the tree is alive, it absorbs nutrients through the soil and delivers them to the entire tree, similar to the way a drinking straw delivers liquid to a person’s mouth. The beauty of the biological process is that it nourishes the tree by allowing the water and nutrients to move quickly up and down but not evaporate out of the sides of the tree, in a similar fashion that a straw delivers liquid quickly up and down, but does not diffuse out the sides. The end grain of the board absorbs liquids, such as stains and dyes, quickly and at a much larger rate than the side grain of the board. Because of this, when applying a colorant such as wood stain or dye to a board, the ends will look darker when compared with the side grain. To get that extra comment about the beauty of your piece, there are a few choices to fix this problem.

One easy fix when sanding your piece is to use a higher grit sandpaper on the end grain than on the side grain. When moving from a coarser grit to a finer grit sandpaper, you are removing the larger surface imperfections into which the color will settle. This will close off the pores in the end grain more, and make the surface look more uniform.
Another choice would be to use a thin 1 to 2 lb cut of bleached-blonde shellac on the end grain of the wood. This will form a thin surface barrier, limiting the penetration of the stain or dye. Be sure to use painter’s tape on the surrounding side grain to avoid bleeding of the shellac onto it.

A third option would be to take a portion of the color you are using and dilute it in appropriate solvent (please see the manufacturer’s guidelines for this information). Use the diluted color on the end grain and reapply until the color match is to your satisfaction.

As a final choice, you can increase the viscosity of a stain or dye if you mix your own by selecting a thicker solvent such as linseed oil or tung oil. These will have a higher viscosity than using a mineral spirits or naphtha base. Making a thicker blend of your color choice to apply to the end grain will slow down absorption and keep the color of your piece looking uniform.

All of these fixes can be used in combination and do require some experimentation with leftover stock from your project. My hope is that by showing you how to pay attention to the fine details such as this, you can bring your craftsmanship to the next level.

Until next time, remember to keep in mind that your favorite piece should always be the one you’re working on, and your best piece will be your next one.

---by Mike Melofchik
- Owner, Dream Forest Studios