OIL FINISHES:
The two oils commonly used in the manufacture of oil finishes are linseed oil and tung oil. Linseed oil is derived from the flax seed, while tung oil is extracted from the nut of a tung tree. Without further treatment, these oils would dry too slowly to make them suitable as modern wood finishes.
Metallic driers are added to Linseed oil, which is then heated, resulting in product commonly known as Boiled Linseed Oil (a misnomer). Tung oil is heat treated to achieve polymerization (a state in which the molecules are bound together in long strands).
After experimenting with many oil finishes in search of a product with desirable characteristics, Liberon Finishing Oil (a tung oil-based product imported from England), was selected as the best oil finish. It seems to have a shorter drying time than other oil-based finishes. Minwax Antique Oil Finish (in the red can) also provides acceptable results, although it does not dry as quickly as Liberon Finishing Oil.
NOTE: It should be noted that an oil finish, while very suitable for the exterior of fine furniture projects, is not recommended for the interiors of cabinets, drawers, et al. Even with ample air circulation, an oil finish will not cure properly, and an unpleasant odor will linger long after the project has been completed.
SPONTANEOUS COMBUSTION:
Before describing the process of applying an oil-based finish, a discussion of spontaneous combustion is warranted. Simply stated, spontaneous combustion describes [oil-soaked] materials bursting into flame: a very dangerous condition that should be avoided at all cost.
Three components are required for combustion:
• Fuel
• Oxygen
• Heat
An oil-soaked rag provides the fuel, and there is abundant Oxygen in the atmosphere. As oil products polymerize, all of those little molecules racing around and bumping into each other generate heat. A rag lying flat readily gives off this heat to the atmosphere and combustion temperature is never achieved. However, in a folded rag the heat is not allowed to dissipate -- it is concentrated in folds and pockets, and the temperature continues to increase until combustion is achieved.
Because spontaneous combustion is so likely, and the dangers so severe, caution should be exercised to prevent an occurrence. This is achieved by closely monitoring all oil-contaminated products during use (never leave an oil-saturated applicator unattended), and by promptly disposing of oil-soaked rags, unfolding them and spreading them flat on a concrete or dirt surface, away from all combustion sources, until completely dry.
When the oil has thoroughly dried, you are left with a “rag Frisbee” that can be safely placed in a trash container.
APPLYING AN OIL FINISH:
OVERVIEW
Applying an oil finish with wet-or-dry sandpaper creates a slurry of oil and sawdust that will fill the pores of open-grained wood; properly applied, a sanded-in oil finish will achieve a glass-smooth surface. One of the benefits of an oil finish is that there is no need to finish an entire project at once, or to maintain a wet edge. You can stop and start as you please, as long as you thoroughly remove excess oil before it becomes thick and unworkable.
After dry-sanding to 220-grit, prepare silicon carbide wet-or-dry sandpaper in three grits:
• 220-grit
• 320-grit
• 400-grit
MATERIALS NEEDED
• Finishing oil
• Silicon carbide (wet-or-dry) abrasive cut or torn into eighths, and folded in thirds.
• Clean, lint-free, absorbent rags (old t-shirts work well).
THE APPLICATION PROCESS
Wet the wood surface with finishing oil, rubbing it in with your hands until the surface fibers are saturated. I keep my finishing oil in a squeeze bottle (with an airtight lid), for easier and better-controlled application.
Start with 220-grit and sand the oiled wood, with the grain, until a slurry of oil and sawdust is created. Once a slurry has been created you can sand in circular or figure-eight patterns. Work one small area at a time, until the surface is consistently smooth and the slurry has been packed into the open pores of the wood.
After several minutes, the surface(s) you have been working will be consistently sanded to 220-grit, and the slurry will have begun to thicken. Next, wipe all remaining slurry from the surface of the wood with a clean, lint-free, rag. This needs to be accomplished before the product becomes too dry and gummy to remove easily - with Liberon Finishing Oil you have about twenty minutes. With other oil finishes, such as Minwax Antique Oil Finish, you have a little longer - perhaps three-quarters of an hour.
You will need to monitor your project for bleed-back over the next few hours. Bleed-back is the term used to describe residual oil that will ooze up to the wood surface from the pores as the finish polymerizes. Bleed-back will appear as small dots of finish on the surface of the wood.
Inspect your work once an hour, wiping away bleed-back with a clean rag. Then allow the first coat to dry for 24 hours before proceeding.
After waiting a full day, repeat the process with 320-grit. Following another 24-hour curing period, repeat the process with 400-grit, and allow the oil to cure for at least a week before applying two thin coats of hard paste wax, waiting five or ten minutes before buffing with a clean, white, lint-free cotton rag (old t-shirt).
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Please let me know if you have questions.
