Cutting Board Finish
Mineral oil is an excellent finish for cutting boards and working wood countertops. It is a particularly good finish when combined with another petroleum distillate, paraffin wax (some use beeswax for its more pleasing odor). Mix one-part melted wax with 5 to 7 parts warm mineral oil and brush or wipe the liquid over the surface. When the mixture solidifies, scrape away the excess wax. Periodically, when water no longer "beades" on the surface, renew the finish with an application of straight mineral oil. Just pour on a liberal quantity of mineral oil and go to bed. In the morning wipe off any oil that was not absorbed into the wood and you're good to go. From time to time you may also make another application of the heated oil/wax mixture. This "finish" has the advantage of not forming a cured film so it will not be damaged by cutting. It is also very easy to renew. Use the mineral oil from your local grocery or drug store. Do not use the scented stuff, a.k.a. "Baby Oil". Commercial finishes that are actually mineral oil include many of the the so-called "Butcher-Block Oil Finishes", and a number of the "Teak Oil" products on the market; though some "Teak Oil" is simply boiled linseed oil. (There is no such thing as oil from Teak. Teak is naturally oily, but teak is not processed for its oil.) Avoid "Butcher Block Oil" and "Salad Bowl Finishes" that are actually varnish.
The remainder of this article is intended for those who would like some additional reading to help understand why mineral oil and paraffin work well in finishing cutting boards, working wood countertops, and wooden kitchen implements. We will also look at some wood species that work well in these applications.
When using this cutting board finish we need to keep in mind that the objective is not to “seal” the grain (the pores); at least not in the traditional sense of that term. The ultimate objective is to fill the pores with oil. That is the primary reasons for using mineral oil in the first place. Since mineral oil is “non-drying” (it never cures), will never go rancid and it doesn't evaporate, over time as we continue to add oil, much of the oil will soak deeper and deeper into the cell structure of the wood and will eventually fill the cell cavities. When that point is reached the countertop will be totally “water proof”. From then on we will only have to “oil” the countertop to replenish the oil that we wipe and/or wash from the surface. The wood below the surface will be permanently filled with oil.
Mineral oil also has the advantage of not forming a finish film; therefore it will not be damaged by cutting—it will never flake or peel from the surface. But, since it does not form a “cured” film, it is fairly easily wiped from the surface. The same wiping that removes waste from the countertop will also remove some of the oil. Since the oil remains a liquid (it never cures), that which is not removed by normal contact will continue to penetrate into the grain structure of the wood until it sinks out of sight.
If you have ever had the opportunity to examine a very old butcher’s block (I’m talking the real deal from a butcher shop, not some countertop pretender) you will notice immediately that the wood has an “oily and waxy” feel, even if it has not been used in years. This is because, over time, the cell structure of the wood has become infused with oil. This oil infusion is our objective in applying the mineral oil/paraffin wax finish. The difference is that we want to use oil that will not go rancid in place of the fat in the meat, and we want to fill the cells structure quickly since our wooden countertop or cutting board will not get the use of a working butcher block.
We also want to avoid any finish that will “seal” the grain since that would be contrary to our ultimate objective of filling the cell structure of the wood with oil. It is true that applying a "sealer coat", for example thinned varnish, an oil/varnish blend, or shellac, will cause the oil will remain on the surface; and, since mineral oil does not evaporate, will give the surface an “oily” appearance for much longer. This will give the illusion of having solved the problem. But, we will have solved the wrong problem. The oil won’t be doing what we want it to do—it will not be “penetrating” into the cell structure of the wood. We will have simply initiated an endless maintenance cycle—we will forever have to apply oil to the countertop. Further, if we do any cutting on the surface we will soon damage the film finish that we used as the "sealer". When that happens, even if no flaking is evident, the surface will become "blotchy" as the oil is now able to penetrate through the finish film in the damaged areas but will not penetrate where the film remains intact.
This begs the question, if the primary objective is to fill the cells of the wood with mineral oil, why do we recommend a blend of mineral oil and paraffin wax? What’s the point of the wax? The point of the wax is to give “temporary longevity” to the finish—a sort of “look-I’ve-done-something” sense of accomplishment, but without preventing the oil from soaking into the cell structure of the wood. As we all know (I hope we all know) “wax” offers virtually no protection against anything; certainly not against moisture, either liquid water or water-vapor (unless it is caked on thick). It doesn’t make any difference if the wax is beeswax, carnauba wax, or paraffin. But, wax will remain on the surface (it doesn’t soak in) and will produce a temporary “film” that will “plug” the pores, cause liquid water to “bead” thus giving us the “feel” we want. The wax in this mixture takes the place of the tallow that was added to the butcher’s block by cutting meat. But, the real work is done by the mineral oil as it continues to soak into the cell structure of the wood. Wax in the mixture simply extends the time between reapplication in the early stages of "seasoning" the countertop or cutting board.
Now, let's briefly focus our attention of the choice of wood for your countertop or cutting board. While any wood can be used, some won't work as well as others because their cell structure will increase the effort required to keep them properly "finished", or they will be so soft that they will quickly become damaged in daily use. The ideal selection will be a heavy, dense, diffuse-porous hardwood with very small pores. Hard maple is an excellent choice and is the most commonly domestic lumber used. Cherry will also work very well, as will a number of tropical hardwoods. Look for wood species that exhibit uniformity in cell structure and density. Avoid wood species that lay down alternating rings of earlywood and latewood that exhibit different density and containing cells of different size. Very open grain, ring-porous hardwoods such as oak, ash, hickory and species with similar grain structure should be avoided. Semi-ring-porous species such as walnut can be used; but, they will require more maintenance.