Rediscovering the natural beauty of wood with sustainable, non-toxic, zero-VOC natural oils and solvents.
This is one of a four-part series on natural, non-toxic, eco-friendly wood finishes.
In the process of building a sustainable and eco-friendly casket company, we’ve had to learn a lot about eco-friendly wood finishes. The “Plain Pine Box” appeals to only so many. We’ve learned how to achieve a wide variety of beautiful wood finishes without using harmful chemicals. Most of our learning has been a matter of rediscovering the historic techniques mastered by 16th century English craftsman. In this article we’ll briefly cover the history, chemistry, and useful techniques for achieving natural oil finishes with natural solvents.
Natural oil finishes date back many centuries. Some natural oils used on wood include linseed oil, tung oil, and walnut oil. Olive oil, almond oil, and coconut oil are also effective for small wood restoration projects. Although, these food grade oils may be a little expensive for large projects. Chinese craftsmen have been using tung oil, produced by pressing the leaves of the tung tree, for more than 1,000 years to seal wood and masonry surfaces. Sixteenth century English craftsman used linseed oil obtained from the dried, ripened seeds from the flax plant—a cereal grain. Natural oil finishes work by penetrating the wood grain surface and oxidizing with exposure to air forming a hard, sealed, protective wood surface. This is different from a conventional polyurethane or varnish that builds up a protective surface on top of the wood.
Natural oil finishes are best applied when thinned with a solvent. If you don’t thin some of these natural oils, it will take days (or weeks) for the oil to dry and the oil will not penetrate the surface as deeply. The solvent helps the oil penetrate the wood grain for a long-lasting protective finish. The solvent will evaporate almost completely as the oil cures. Natural oil finishes can be thinned with conventional solvents or eco-friendly solvents like orange oil or good ol’ lemon juice.
The paint aisle in your local home improvement store will have at least six different varieties of conventional solvents. All of these contain VOCs (volatile organic compounds). Turpentine is a common solvent obtained by distilling the resin of pine trees. Paint thinners, also known as mineral spirits, are distillates of petroleum. Notice the warnings on these solvents; they are toxic, require ventilation, and are flammable. There is an alternative that smells nice, won’t give you a headache, and is stable (no VOCs). Citrus solvent, also known as orange oil, is made by distilling the peels of citrus fruit—mainly oranges. Orange oil is used in commercial food flavoring. It is a pleasure to work with—and it smells like oranges!
Mixing orange oil one-to-one with tung oil yields an effective natural wood finish with zero harmful toxins or VOCs. Applying the oil mixture with a foam brush or chip brush is easy for even a novice woodworker. Unlike conventional varnish, the finish is forgiving of drips and runs. Apply heavily on fresh (sanded) wood surfaces for deep penetration in the wood grain. Within 30 minutes touch up areas where the wood has absorbed the oil and smooth out where the oil is pooling. Apply multiple coats for more protection with light sanding between coats with 300 grit (or finer) or #00 steel wool. We like to wait 24-48 hours between coats.
Tung oil brings out the natural character and colors of wood on oak, cherry, and pine projects. Tung oil will add a light yellow hue, or “honey glaze” to the wood bringing out those warm tones of red that naturally occur in the wood grain. Linseed oil works almost the same, but will yellow a little more over time than tung oil. Walnut oil darkens over time—especially on red oak resulting in a very rich dark reddish-brown color. Walnut oil is naturally thinner and can be applied without a solvent. Walnut oil is also a good food grade surface treatment for cutting boards or kitchen countertops.