Choosing an Effective Wood Finish

La Collina End Grain, "Butcher Block" Cherry Board

I give a lot of thought to the finish I apply to my work. This is generally the last step before I complete a project. In addition to enhancing the natural beauty of the wood, the right finish should offer some protection from the elements, scratches and day-to-day use.

Below I describe why I choose certain finishes and the results from a brief (somewhat scientific) )"torture" test that I conducted to illustrate how some of these finishes hold up under certain conditions.

What Type of Finish

How a piece is to be used and the nature of the wood determines what kind of finish I apply. There are essentially two kinds of finish, a film finish and a penetrating finish.

I (almost always) prefer a penetrating finsh.

A film finish sits on top of the wood. Polyurethane, lacquer and shellac are considered film finishes. Once they dry, they create an effective protective barrier from stains. They are durable and offer effective protection, but they wear off over time, may chip or scratch, and are generally more challenging to restore, often requiring sanding and reapplication of the finish. In some cases, particularly when working with textured surfaces, I will apply a spray lacquer to decorative items that are not handled on regular basis.

A penetrating finish penetrates below the surface and the oil dries or "polymerizes" within the wood. Moderate scratches won't expose an unprotected surface and these wear marks are easily dealt with by reapplying a wood conditioner.

Oils that I DON'T Use...

I never use a vegetable oil (olive, coconut, culinary Walnut Oil, et al.) on wood since these oils may darken the wood surface over time, go moldy, or turn rancid. Food grade mineral oil does not spoil like vegetable-based oil, but it also never dries, so I do not use this as a primary treatment.

Oils that I DO use... (It depends)

Bowls

For my Bowls I apply several coats of Walnut oil. Heat-treated to remove the proteins which may cause allergic reactions, Walnut oil polymerizes over time – it dries inside the wood rather than just sit on the surface. This is not the case with culinary Walnut oil.

Boards

I generally treat my utility boards, cheese paddles, live-edge and end grain serving boards with several coats of a blend of pure Tung oil* and a natural citrus solvent. Like Walnut, Tung oil is a drying oil; it polymerizes. Thinning it with a citrus solvent permits the Tung oil to penetrate deep into the wood surface. I apply as much as the wood will absorb, giving it a few weeks to dry, with sanding between coats. This finish enhances the beauty of the wood while building up a very effective moisture barrier.

I might apply as many as four coats of this finish my boards and then topcoat each item with our "Cera della Nonna" wood conditioner. This is a great blend to restore a finish that has worn off as a result of normal hand washing. I use 100% organic Brazilian Carnauba wax, beeswax from our own hives, and food-grade mineral oil in this recipe.

The primary finish (green, below) soaks into the wood and the topcoat conditioner (blue) adds a layer of protection that can easily be renewed. In end grain boards (below, right) the cell structure acts like straws and wicks the oil deep into the board. In side or long grain boards, the oil does not penetrate as deeply.

Oil Finish Penetration: Side Grain versus End Grain

Handled Utility Items

I finish most of my unpainted turned items (ice cream scoops, pens, cheese knives, salt and pepper shakers and mills) with a friction polish after they have been sanded smooth. The friction polish is applied to the wood while it is still spinning on the lathe so the heat/friction quickly hardens the finish. I consider this to be a durable film finish. It is important that these items never visit the inside of a dishwasher where the heat will, at the very least, degrade the surface finish. After gentle handwashing, regular applications of our wood conditioner will help to maintain these items by creating a moisture barrier.

For painted utility items (ice cream scoops and bowls) I use several coats of Hemp oil. Hemp oil is an excellent, non-toxic penetrating finish which does not tend to darken light colored woods or painted surfaces. I then apply a non-toxic wood conditioner..

How effective are these finishes?

I recently conducted a "torture test" using several different oil/wax finishes that I use. I treated three species of wood (Walnut, Cherry and Maple) with each finish.

The wood was sanded to 220 grit prior to the test. I applied each finish, waited two weeks and reapplied. I applied a total of three coats and then let everything cure for one month.

My goal was to subject each test square to a variety of worst case liquids that might be encountered in the real world. I chose water, an acid (6% vinegar), a base (1 tbs. baking soda in 1 cup water), strong alcohol (200 proof), and red wine (a nice Syrah!) to test staining.

Test squares with liquids applied. Top to bottom: alcohol, acid, base, red wine, water.

All of the liquids were at room temperature and – to keep it simple – allowed to remain on the wood for 60 minutes.

Test Results:

The 200 proof alcohol flashed off too quickly to have an effect on any of the samples. Perhaps a lower alcohol content would have been a better candidate as it would have taken longer to evaporate.

Starting from the bottom of the pack...

Mineral Oil

Significant lightening/bleaching from the water and vinegar. Staining from the red wine and darkening from alkaline reaction with the wood's natural tannins. There was little visible beading and the liquids were pulled along the grain of the wood (see the Maple+red wine at the far right).

Cera della Nonna

Each of the liquids beaded nicely on this top coat wood conditioner, but extended contact resulted in similar results to the mineral oil test square with staining and bleaching and wicking by the wood fibers. I only use this non-polymerizing finish on top of the primary, penetrating finish.

Walnut Oil

There was slight bleaching with the water and vinegar, and significant staining with the alkaline solution and red wine on both the Cherry and Walnut samples. Little wicking suggests that the wood's pores were already somewhat filled with polymerized oil.

Tung Oil

The Tung oil offered by far the best protection. There was some very slight bleaching with wine and vinegar, but no discernible tannin reaction.

(I did not include Hemp oil in this test, though I suspect it would have taken Second Place just behind Tung oil.)

Conclusions:

Overall, I was pleased with these results. The application and cure time for Walnut and Tung oils is justified by these findings. Once these food-safe oils have cured it is not difficult to keep these items in good shape.

Keep wooden items out of the dishwasher. A gentle hand wash with warm water and mild soap, and then a quick towel dry will maintain your special item. Restore the wood periodically with our "Cera della Nonna". The impressive beading (below) indicates that it is an effective topcoat when applied after gentle washing and drying.

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*Beware of “Tung Oil Finishes” that you may find in your local hardware or big box store. Many of these contain some Tung oil, but also contain other additives and petroleum distillates. They may require less care and time to cure, but read the label to determine if they are safe enough for your needs.