An important point to remember when selecting ANY woodwork finish is that no finish will last forever. All finishes will need to be refreshed or redone at some time in the future. Some finishes need to be re-done as early as 3 months, others can take 30 to 40 years or more before they need refreshing or redoing. The purpose of this article is to give new woodworkers some sort of a head start in trying to assess what direction they might want to go when it comes to finishing their woodworking projects and there is much more to learn.
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So what decides whether a finish needs to be redone or refreshed? Whoever owns the piece at the time, if they are not happy with the finish, needs to be refinished for any number of reasons. Sometimes the woodworker used "green wood", full of water and as it dries it can lift off some finishes, maybe the finish has been worn off in patches just from normal wear and tear like chairs and dining tables, maybe the finish is just old, crackled or dull and has lost its luster, then it may be time to refresh it, so lots of different reasons and circumstances.
Dyes and Stains
The first step in finishing might be to apply a colorant to the wood, often called a stain but could also be a dye such as an aniline dye.
Stains are typically pulverized dirt or clays in different earth tone colors, mixed with some sort of water or oil/solvent solution then painted on with a brush, and sometimes wiped off a short time later after some of the colors have had a chance to penetrate the wood. Stains are very resistant to UV light and are therefore perfect for building siding and fences. They are not as good for enhancing the grain structure of figured woods because the pulverized dirt, some of which stays on the wood, even after wiping off, forms a thin layer of pulverized clay which normally masks the special features of the woods to varying degrees.
Wood dyes, often called Aniline Dyes are often created synthetically, often from coal tar, which makes them a transparent color. Because dyes change the color of the wood without "masking it" they are ideal for figured woods like Tiger, Birdseye, Burls, and all other similar figured woods and designs. Aniline dyes are color-fast products but are much less UV resistant than stains, so using them for outdoor projects is not recommended. Aniline dyes come in a wide range of colors and tones.
Aniline dyes can be purchased as liquid concentrates or as powders and can often be mixed with either water or some form of solvent like paint thinners or oils. Because of the semi-transparent properties of aniline dyes, they are preferred for working with figured wood as they typically allow the vibrancy of the wood to show through.
Anyone who works with "figured woods" (that are often quite expensive to purchase) like Tiger or Birds eye Maple or Oak, will want to retain that figure in their projects. The figure in many kinds of wood is an anomaly where the wood grain grows in conflicting angles and it creates a sort of optical illusion or "movement" of the wood. These kinds of wood are said to contain a "Chatouance" and are defined as "having a changeable luster or color with an undulating narrow band of white light or a gem-like appearance like a cat's eye." If you wish to change the color of lighter woods, you will want to use dyes rather than stains as the stains will often leave a thin layer of earth material on the wood which is what stains are made from whereas dyes will allow the luster of the wood to penetrate the transparent dye.
Unfortunately, there is just not the space or time to talk about the wide variety of finishing products in this article, but anyone who wishes to learn more can research books and online articles on those aspects for more information.
When I think about many of the more popular woodworking finishing products, I break them down into 3 categories.
The film finishes, like Polyurethane, Varathane (the same type of thing as Polyurethane), Lacquer, and Varnishes.
Oil finishes such as Tung Oil, Walnut Oil, Linseed Oil, and Mineral Oil, are all true oil finishes.
Hybrid finishes include Danish Oil, Teak Oil, Antique Oil, and similar products.
These types of common finishes are so named because they leave a thin film of finish material on top of the wood to which they are applied. They are often waterproof and are resistant to spills as normally the film "seals" the wood, making it quite strong and wear-resistant at the same time. Film finishes are great around food and eating areas as they are easier to clean up after and help to preserve the wood.
Film finishes are both oil and water-based and in both cases come in Glossy, Stipple, or Satin and Matte. The glossy product is clear while the satin and matte versions often contain finely ground silica that gives the visual appearance of a semi-gloss or full dull matte finish. The disadvantage to most film finishes is that when they need to be refreshed, such as the varnishes and polyurethanes and Varathanes, they need to be scraped and/or sanded off and then re-applied. Lacquer finishes are most often sprayed and petroleum-based Lacquers and some water-based can be reapplied over top of itself as the top layer melts and blends into the lower layers.
The true oil finishes are made from vegetable ingredients. Oil finish products break down into a couple of categories, Hardening Oils and Non-hardening Oils. Nonhardening oils are often used on cutting boards as they are normally rated as "food safe". Nonhardening oils would be Raw Flax and Linseed oil, Walnut Oil, Mineral oil, and many others. These raw oils often take a LONG time, like days, weeks, and even months to dry and harden, which is why they are not great for furniture or similar applications.
The hardening oils are what you want to use for woodwork finishing because they will often dry and at least harden well enough to re-finish overnight (depending on the environment) Tung Oil is derived from the oil of the Tung Nut, Linseed oil is nothing more than Flax Oil. Cold pressed from flax seeds, it is called Raw Flax Oil in the health food store and referred to as Linseed Oil in the hardware store. Raw Linseed Oil can be used as a finish but takes a LONG time to dry and harden which is why most Linseed Oils are called “Boiled”. Boiled or Double Boiled Linseed Oil which often dries overnight and can be re-applied the following day. Linseed Oil is no longer “boiled” but it is heated up to a high degree which is called “Polymerizing” this heating process changes the molecules in the Linseed Oil which allow it to dry quicker.
Oil finishes are very easy to apply but are not waterproof, they are water resistant for a time, depending on the number of layers and type of product but if water or liquid is left on them, it will typically soak into the wood. Oils do not offer a high degree of protection of the wood from marks, scratches, bumps, and day-to-day wear such as chairs and dining tables, but on the other hand, they are easy to fix and re-finishing a wood project that has been oiled, only means re-applying a new coat or 2 over top of what was done previously. Very easy to work with.
A more recent (within the last 20 years or so) addition to the Oils also called hard wax oils are a type of hybrid that include oil finishes with some additives, like natural waxes and drying agents. Some that come to mind are Osmo, Odies Oil, and Rubico.
These newer oils have much the same characteristics of the true natural oils, but offer better protection and can be re-applied on top of earlier coatings as the coating blend together.
One of the disadvantages of oils is that it is difficult or impossible to get a high gloss finish with them if that is your goal.
The hybrid finishes including Danish Oil, Teak Oil, Antique Oil, and others are very difficult to describe the ingredients because they vary between manufacturers and even within manufacturers. For example, Danish Oil is not really an oil at all, in many cases it is a mixture of one-third Varnish or Polyurethane, one-third oil, like Tung oil, and one-third a solvent like turpentine or ordinary paint thinner, oh and sometimes aniline dye is thrown in to give it some color. So why is Danish Oil not an oil? Because the varnish or Polyurethane that is contained in the mixture adheres to the surface of the wood, just like any other "film finish" and this prevents future re-finishing with oil-based products like Tung or linseed oils, from actually penetrating that film finish, these re-applied oils just "sit" on top the varnish layer and never really dry or harden properly as they can never penetrate the wood fibers, so you can end up with a bit of a sticky mess to clean up and end up re-surfacing like a film finish. Sand and re-do.
The same is true with Teak Oil, made by a number of manufacturers who do not disclose the contents, Teak Oil is often some blend of Linseed oil, some driers, and other additives, possibly some form or varnish, actual contents unknown. Antique Oil is also another made-up oil that may or may not contain any number of ingredients and or dyes.
The advantage of the Hybrids, they can be applied easily, they often look very good, and offer some degree of water resistance but little in the form or wear and tear. In terms of usage, as long as you know what you are getting with these, they are fine to use, just be aware the refinishing in the future may be different than what you think.
One of the "painters secrets" is something called Japan Dryer, it's available in most paint stores and comes in a variety of sizes. For most woodworkers who are using smaller amounts of finishing products the smallest size is often sufficient. The dryer consists of a dark liquid, and the bottle states that it speeds up drying time and toughens the finish of oil-based enamel paints and vanishes. (apparently, it is especially useful if the weather is damp or cool) My research also revealed that they claim the dryer will also slightly darken the color. I recently tried it with Tung oil and could not detect any color difference between "dried" Tung oils and "non-dried" Tung. I also found the speed up of Tung oil by itself was small. I would normally allow this to dry overnight anyway before re-coating so it didn't really make a difference to me.
I have not tried this product with Osmo, that will be for a future experiment.
Mixing instructions are for 7.5ml per 1 liter or 30ml per 3.78 liters.
Since I did not want to mix a large quantity of the dryer with my finishing product, I worked backward smaller quantities because I am often finishing smaller items.
In terms of the mixture, the bottle says
7.5ml to 1 Litre or 0.26 oz to 35.1 Floz
To break this down further I did this math, but it's working double checking
3.75ml to 500ml or 0.13 oz to 17.6 Floz
1.87ml to 250ml or 0.06 oz to 8.8 Floz
You could break it down even further if you need
All in all, it's always up to the woodworker that needs to determine what is best for their project and what kind of a look they want to have, and how long they think they will last. I have a trunk from that my Grandfather built around 1912, making it well over 100 years old now. It has some sort of paint over the wood and because he was a Blacksmith and not a woodworker, although he did ok there too, it is edged with tin. I don't dare try to refinish or restore it, I would lose too much patina, it's beautiful the way it is and it's now a family heirloom ...
Copyright Colin Knecht
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