Finishing Touch: Penetrating oil finishes
Film finishes are great when you need maximum durability, such as on table tops, floors, handrails, cabinet doors and countertops. They offer the greatest resistance to abrasion, wear, water, water vapour and heat. They cure hard, which makes them very durable. But they can be somewhat challenging to apply, and difficult to repair. They also dry slowly, making the work surface susceptible to dust nibs.
For woodworking projects that don’t get a lot of daily wear and tear – picture frames, jewellery boxes, display cabinets, sculptures, turnings, trimwork and the like – penetrating oil finishes can be an excellent choice. They leave the wood looking natural, and do a good job of bringing out the detail in wood grain. As well, because these finishes don’t crack or peel they’re great for wooden objects that are in contact with food (such as cutting boards, salad bowls and kitchen utensils) and for toys that end up in children’s mouths.
Another advantage of penetrating oil finishes is that they have very low levels of VOCs (Volatile Organic Compounds) or are VOC-free. Film finishes, on the other hand, typically contain petroleum- and chemical-based solvents, and usually heavy metal dryers.
All penetrating oil finishes permeate wood surfaces by means of capillary action and then self-polymerize (harden) by means of oxidation (exposure to air) through a reaction known as crosslinking. They don’t cure as hard as film finishes, and some always remain soft.
There are three types of penetrating oil finishes: pure oil, polymerized oil, and Hardwax oil. Things can be a bit confusing when choosing one of these products, so read on.
Tung oil, along with linseed and walnut oil, are the only three true natural pure oil finishes available. They tend to dry slowly, though polymerized versions of these finishes are available, which dry faster and have better abrasion and moisture resistance. (Photo by Lee Valley)
Safe For Everything
While you’ll find petroleum distillates, solvents or heavy metal driers in many finishes, Tried and True’s ‘Original Wood Finish’ and ‘Danish Oil Finish’ don’t have any of those ingredients, making them safe for all applications. (Photos by Lee Valley)
New to Many Woodworkers
Hardwax Oil, which is what OSMO products are, have been around for a long time, but are still relatively new to most North American woodworkers and DIY'ers. These products have a lot going for them.
Saicos Hardwax Oil
A natural plant oil and wax based finish that can be applied to many surfaces in a home and on furniture. (Photo by Saicos / Raincoast Alternatives)
Also available in many colours, ‘Kunos’ by Livos is a blended finish that can be applied to interior millwork, furniture, floors and more. (Photo by Livos)
Also referred to as raw, straight, true or 100% oil, pure oil can be made from linseed oil (derived from flax seed), tung oil (extracted from nuts of the tung tree – Vernicia fordii), or walnut oil (from the walnut tree, Juglans regia). These really are the only ‘natural’ oil finishes that are completely ‘chew-safe’, making them ideal for toys that can end up in children’s mouths. There are polymerized versions of these oils that we can also include in the natural finish category as well. (see ‘Polymerized Oil’ below).
Pure oils need to be applied on bare wood, allowed to sit for around 15 to 20 minutes, and then wiped off. You need to apply multiple coats to get any level of protection – 6 to 8 coats isn’t out of the question – with each coat allowed to dry between applications. Depending on the relative humidity in your shop this might take several weeks, or longer. All pure oils dry to a satin finish.
Linseed oil is the slowest to dry and it cures soft. It gives an amber hue to wood that tends to darken over time. It can also develop mold if exposed to humidity. Tung oil imparts a light golden colour, doesn’t yellow as much as linseed oil, cures harder, has better moisture resistance and won’t mold, which makes it a better finish than linseed oil. However if a tung oil product has a solvent listed on the container it won’t be pure tung oil. In fact, unless specifically listed as an ingredient, the finish may not contain any tung oil at all. Minwax Tung Oil Finish, for example, is made from an oil (probably linseed) blended with varnish and mineral spirits, and doesn’t contain a drop of tung oil (see “Oil/Varnish Finishes” Sidebar). Walnut oil gives a finish similar to tung oil and is also moisture resistant. Of the three pure oils it’s the least used, likely because it’s not widely available, and provides no real advantages over tung oil.
Pure oils polymerize on their own, but they do it slowly. To speed up the process manufacturers heat pure oil in an oxygen free environment that creates a chemical change – oils that undergo this process are marketed as Polymerized Oils. This somewhat increases the oils abrasion and water resistance and gives a high lustre and glossier sheen to the finish. Polymerized oils generally don’t contain metallic dryers, so they can be considered a natural oil, making them food-safe. Some manufacturers add a wax to polymerized linseed oil to enhance the sheen of the finish. Once a polymerized finish has fully cured it is safe to use in contact with food (as are virtually all other wood finishes).
Not all polymerized oils are labelled as such. Tried & True’s ‘Original Wood Finish’ contains polymerized linseed oil and beeswax. Their ‘Danish Oil’ contains only polymerized linseed oil. Watco’s ‘Danish Oil’ contains a penetrating oil (probably linseed), mineral spirits, and naphtha. The Lee Valley polymerized oils don’t contain any additives.
Blended natural oil
Manufacturers add various substances to natural oils to enhance abrasion and water resistance, and speed up both drying and curing. Similar to Pure and Polymerized oils these can be considered penetrating oils. ‘Universal Wood Oil’ from Livos, for example, contains linseed oil, natural resin glycerol ester, orange oil, isoaliphates, silicic acid, micronized wax, dehydrated amino sugar, and lead-free drying agents.
Hardwax Oil is another type of blended oil. They’re somewhat a new class of finish, at least for North American woodworkers, though they’ve been common in Europe for decades. They’re made of vegetable oils that penetrate the wood surface, waxes that sit on the wood surface and produce a water resistant film, and mineral spirits as a solvent. Some contain lead and cobalt-free metallic dryers. Saicos is a brand of hardwax oil that’s available in Canada. For more information on these finishes read “Hardwax Oil” in our Aug/Sept 2019 issue.
Blended oil finishes do emit some VOCs while drying. They dry fairly quickly and cure at about the same rate as polymerized oils, producing a highly durable, moisture resistant finish. While these aren’t chew-safe finishes, once cured they are food-safe. Many of these oils are suitable for exterior use.
Teak oil doesn’t exist. The seeds and wood of the Teak tree (Tectona grandis) aren’t processed for oil. What you see advertised as Teak oil contains a mixture of some other oil (typically linseed or tung) mixed with varnish and possibly a metallic dryer. Essentially these are oil/varnish blends, which you can easily and more economically make in your shop. For more information read “Shop Made Finishes” in our Feb/Mar 2019 issue.
Mineral oil is a petroleum distillate that doesn’t oxidize, so it doesn’t dry. Some woodworkers use it to finish toys, kitchen utensils, and wood countertops, as it’s non-toxic, clear (non-yellowing), odourless and somewhat moisture repellant. However, it provides no abrasion protection, is easily rubbed or washed off and requires constant replenishing. Adding wax to the oil does little to improve its durability. Either tung or linseed oil offers better protection.
Blends of oil and varnish have been around for quite some time. They’re somewhat of a hybrid finish – part oil finish, part film finish. A blended oil/varnish finish consists of oil (usually boiled linseed or tung), to which is added mineral spirits (as a thinner) and varnish (or polyurethane) in a non-critical ratio of 1:1:1. It goes on just like a penetrating oil finish, but offers greater durability and scratch resistance (depending on the number of coats applied). It’s easy to make your own oil/varnish finish – read “Shop Made Finishes” in the Feb/Mar 2019 issue.
Boiled Linseed Oil
Boiled linseed oil (BLO) isn’t a pure oil, nor is it the same as polymerized linseed oil. BLO is made from linseed oil to which metallic dryers (ions of cobalt, iron, and manganese) or petroleum-based compounds (such as mineral spirits, naphtha, and dipropylene glycol monomethyl) have been added to make it dry much more quickly. It does emit some VOCs while drying, and isn’t the best choice for children’s toys or kitchen utensils.
If you’re looking for a finish to use on anything that will end up in a child’s mouth and for kitchen utensils, then a pure or polymerized oil is a good choice. For anything else, it largely comes down to personal preference and experience – how much time you want to devote to finishing, the tone and sheen you want and the degree of surface protection you’re looking to achieve. Where projects won’t be subject to an excessive amount of wear and tear, a polymerized or Hardwax oil certainly is worth considering. If you’re unsure about what’s in any finish, check the ingredients on the label or, if available, read the product’s Material Safety Data Sheet.