I guess the expression “hand rubbed oil finish” does have something romantic about it. It brings to mind a picture of the master craftsman practicing an ancient technique to reveal the beauty of fine woodworking.

Oil is my favorite finish. It penetrates the wood, creates depth and allows the figure to shimmer. I consider oil as the only finish that allows wood to look natural whilst imparting the rich color characteristic of freshly surfaced wood. One of its biggest advantages as a finish is its simplicity, both in terms of its subtle appearance and ease of application. For those who view finishing as a necessary evil, the wipe-on, wipe-off modern oil finish is perhaps as close as you can come to not finishing at all.

Oil finishes has come a long way since the old days. The old timers who taught me about woodworking rubbed in many coats of boiled linseed oil following the “rule of one”: Once a day for a week, once a week for a month, once a month for a year, and once a year for life! Off course this process will still produce an excellent finish, but “modern” oils are available that requires less effort.

Oil mixtures:
Commercial products like Rustin’s Danish Oil are a mix of oil, resin, driers and a solvent. The natural oils most commonly used are linseed oil, pressed from flaxseed or tung oil, from the nut of the Tung tree. There are many other natural oils but linseed oil and tung oil are readily available.
Resins are solids and add bulk to the oil mixture. In many cases they are the same solids that are used in varnishes. The most common ones are modified alkyds and phenolic resin. Adding resin to the oil results in a harder finish, one that builds film thickness quickly, because the solids fill the pores of the wood more readily than oil alone.
The solvent dissolves all the components of the mixture, reduces its viscosity and makes it easier to apply. It also increases its ability to penetrate the wood. The most common solvent is mineral spirits.

Curing
Most oil mixture includes driers, heavy-metal salts that speed up the drying process. Natural linseed oil and tung oil will dry when exposed to air, but raw oil will take weeks to dry. By adding driers this time is reduced to hours. The driers sometime referred to as “Japan driers”, include zinc, cobalt, magnesium and lead.
Another method used to shorten oil’s drying time is polymerization. Most commercial tung oil products are partially polymerized. The process involves heating the oil, causing a percentage of its molecules to bond, which increases the oil’s viscosity and shorten its drying time.
The term “boiled linseed oil” is a misnomer; it is not boiled at all! Instead it has driers added. Metal salts are added with the help of a chemical catalyst. The reference to boiled is probably a throwback to an early process in which the oil was heated to help dissolve the metal salts.
Boiled linseed oil alone makes a credible finish and there are many purists who will use nothing else.

Application
Oil’s most alluring feature is that it is easy to apply. You simply wipe it on, allow some time for penetration and solvent evaporation, then wipe off the excess. It is almost impossible to get bad results. The amount of oil applied, the speed, pattern and method of application have virtually no effect on the result. You don’t even need a dust free room to get excellent results!
However, because oil don’t hide surface imperfections very well, you must sand to a much finer grit than necessary for surface-coating finishes like varnish. Final sanding should be at least 220 grit, but it may need to be 400 or even 600 for fine grained woods.
Depending on the wood species, the first and even second coat tends to be completely absorbed into the wood’s surface and act as a sealer. Yellow wood will absorb oil easily and quickly; Iron wood will absorb almost nothing. Once the wood is saturated with cured oil, successive coats will start to form a film on the surface. You can get an effect that ranges from a barely perceptive finish in a single coat to a glossy film which can take from two to five coats. Because oil is a reactive finish (once it dries, subsequent coats will not dissolve it), a dried oil finish can be recoated by wiping or brushing, without fear of disturbing the dried layer.
The single most major mistake you can make with oils is neglecting to wipe off the excess before the oil dries. This will result in a sticky mess which must be scrubbed off with steel wool and elbow grease! Neither lacquer thinner nor acetone is a true solvent of cured oil. About the only thing that will dissolve the oil film is methylene chloride, the active ingredient in paint strippers.
A common problem with oil finishes is “bleeding”. On large pore woods, such as oak, there is a tendency for the extra oil trapped in the pores to leach out and form shiny spots on the wood’s surface. This generally only occurs on the first coat or two, until the cured oil seals the pores. Bleeding can most often be avoided by applying the oil early in the day, then rewiping the surface every hour or so until the leaching stops. If the shiny spots are left to harden, there is no way to remove them, except by sanding with 400 grit paper.

Disadvantage
Whilst oil’s simple nature is its advantage, it is also its downside. An oil finish is an inherently weak finish, which wears off easily and has a very low moisture-vapor resistance. Because oil is largely absorbed rather than becoming a surface film, the wood is given very little protection from abrasion or staining. Also, because of its low moisture-vapor resistance, water molecules can penetrate easily, same with alcohol or other liquids. This makes oil a poor choice for wooden objects used in wet or humid conditions.

Repairing and refinishing
Oil’s reactive drying properties and forgiving application qualities makes it a finish that is extremely repairable. A white water ring or damaged spot can be lightly sanded or steel wooled before new oil is applied. Due to its inability to redissolve itself, the freshly applied oil will not affect the undamaged finish in the surrounding area and will blend the spot almost invisibly, even if the finish is years old. So, with oil’s reparability comes a responsibility for maintenance. Ideally, an oil finish should be rejuvenated every year or so, depending on the amount of wear it is subjected to.

Warning!
Oil soaked rags or paper towels are ready prey to spontaneous combustion; if left in a pile, they can heat up and burst into flames on their own accord!
Hang the used rags up to dry or immerse in a bucket of water.

In Part 2 I will look at different oil finishing techniques.