I am a wood turner and woodworker out of Raleigh, North Carolina professionally producing items for well over the last twelve years. This article delves into the types of wood finishes used for woodturning and general woodwork. Bob Flexner’s book “Understanding Wood Finishing”is the best book I have read on wood finishes. Its well worth picking up as it will go more in depth than I will.
Currently I specialize in the creation of asymmetrical, irregular, and off-balance natural edge turned sculpture, urn artistry, functional wood turnings as well as some period furniture. The types of wood finishes that I talk about in this article are mainly suited for those items.
At the time of this writing I have produced several hundred bowls. Upwards of six hundred hollow vessels, and several pieces of furniture. Early on I started the practice of producing items with varying sheens working from several types of wood finishes. Some examples are shown in my portfolio section. Those finishes that I chose adapt easily into what I call “finish building”. This process was born largely from my turning activities but I also adapt the same principles to my furniture projects.
Red Oak Burl Cremation Urn
So why do I do it or what is the aim of building a finish? Originally, I wanted to improve my finishing skills, produce a superior product, and I wanted to develop the best finish for the function of the project. By best I am thinking about the factors that influence item quality. That is appearance, feel, maintenance, and performance of the finish for the piece which it is applied. The finish building requires more time (especially on larger projects), though its not a complicated process. While the differences are subtle, comparing a built finish versus not, you can expect that the evenness of sheen, tactile feel, and overall performance of the object or project will be superior when building your finishes.
Categories or Types of Wood Finishes
These types of wood finishes are divided into a couple categories. Penetrating oils, film finishes, waxes, and sometimes glues (i.e. CA and epoxies). Natural oils, mineral oil and blended oils (i.e. Danish oil and commercial Tung/Linseed oils, etc.) fall into the class of penetrating oils. Penetrating oils soak into the wood fibers and usually do not cure very quickly in their raw state. Some commercial products have chemical dryers added to them to improve the cure rate. Chemical dryers are typically metallic salts of some form, cobalt or manganese salts for example. Across the board, penetrating oils produce minimal finish build. Build meaning the degree of solids that form on the wood surface.
Watco Danish Oil Natural
Higher build rates typically come from blended finishes or some oil and varnish mixture. I have the most experience using Mahoney’s Walnut oil and Danish oil, a formula that I mix myself. Boiled linseed oil and Tung oil finish act in a similar manner to that of Danish oil. Commercial Boiled Linseed oil and Tung oil finish are considered blended finishes. Linseed oil cures very slowly in its raw state, hence the boiling.
Pure Tung oil cures more quickly than raw linseed oil. Sometimes referred as China oil, it comes in a few grades. Some of the lower quality grades are sourced from south America. The highest quality (grade 1) produces a yellow cast oil and cures the quickest. Its cure times are fairly similar to that of Danish oil.
I blend my own Danish oil, comprised of equal parts gloss poly, pure Tung oil, and spirits. This is basically a variant of the finish that Sam Maloof is well known to use. It’s important to use gloss poly as semi-gloss and satin poly have compounds added that chemically reduce the level of sheen and as such you will not be able to build a higher sheen out of these products. Here are some reasons and detailed information for making my own Danish oil.
This finish performs somewhere between commercial Danish oil and wipe on poly. Behaving more similarly to a wipe-on poly as the mixture gets older. Overall penetrating oils are quick and easy to apply and give a minimal durability compared to other more robust types of wood finishes.
Mahoney’s Walnut Oil Finish
To me Walnut oil finish is an interesting product as it is the only raw oil that I have used that develops a surface build. The high acid content and heat treatment influences the surface build. The heat treating improves the degree of cross-linking in its polymer chains. Either way I use it as the finish of choice for all items intended to be for food usage. There is a school of thought that says all finish is food safe once fully cured. Without getting into that debate in this article, I find this finish to be the one of choice for these reasons. If your looking to bone up on utility finishes, find out which food safe wood finishes are worth using.
First is ease of application, nothing beats a penetrating oil for being labor friendly. Not to mention that this finish develops some surface build which helps in its water repelling qualities. Its low sheen, so for an item that is prone to use and scratching, the wear is not as pronounced. Minimal effort is needed to maintain or repair the finish. Maintenance is typical for utility items. Lastly is marketing, even if it is true that a lacquer for example once cured is food safe, its an easier sell to the public that the finish used is a natural product and does not have chemical driers (i.e. heavy metals) added. All in all I consider this finish to be the best choice of finish for items intended to be food safe.
Film Finishes – Polyurethane, varnish, lacquer, etc.
Film finishes as a group are made up of shellac, polyurethane/varnish, lacquers, water base, two-part, epoxies, etc. The film is the build of the finish on the surface of the wood. This is different than the finish soaking into the grain as in the case of penetrating finishes.
Water Based Types of Wood Finishes
Water based, or water borne finishes, are appealing due to the exclusion of petro chemical solvents. They are primarily composed of acrylic and polyurethane resins dissolved in water. In my limited experience I find water-based finishes are thin and would require more numerous coats to develop sufficient surface thickness for rubbing. That is the brushing formulas of water-based finishes I have used, a Stewmac product I believe.
Mohawk Precat Lacquer
As a class of finishes though water-based finishes are rather varied. So, my foray into water-based finishes probably isn’t a just representation of what is offered. For example, there are water-based lacquers that behave like a polyurethane. Meaning each coat forms distinct layers as polyurethane does. In other words, the finish doesn’t “melt in” like traditional nitrocellulose lacquer does. Rubbing of water-based finish therefor has the potential to cause issues. The manufacturer recommends the spraying of water-based finishes.
The term “melt in” refers to traditional lacquers (nitrocellulose) which are evaporative finishes. Meaning the finish cures as the finish or solvent in the finish evaporates. Any new coats applied partially dissolve the previous layer and the evaporation continues. The finish layer essentially is one continuous coat. Catalyzed lacquers (that is post and pre catalyzed) are termed reactive finishes. The curing process is sped up with the addition of a catalyst. The degree of dissolving any previous coats is greatly diminished, by comparison, in reactive finishes.
There are other water based finishes that do melt in, however not quite to the degree of traditional lacquers. Some also take well with the application of a retarder so as to make them potentially viable in a brushing application. Alternatively, some water borne finishes could be considered two-part finishes as they are water based but use the addition of a curing catalyst. So as a product range its all over the place.
All that said, in general water-based finishes tend to not yellow, are easy to clean, no volatiles, short recoat times, and has a decent solids percentage. So, there are definitely some attractive qualities about water-based finishes.
One of the hurdles I have had with water-based finishes, from a woodturning perspective, is the use of spray equipment. I like to run things pretty simple and on a low operating cost basis. Spraying finishes to achieve surface build requires multiple coats, so that is multiple cleanings of spray equipment and lots of overspray. The space required for that as well. Not to mention spraying round objects has a bit of a learning curve. I find the issues true even of two-part finishes. Overall, at this point in time I find it easier to achieve the results I am after with wiping or brushing finishes.
Two part finishes
Two-part finishes, that is conversion varnish, post catalyzed lacquers, etc. I find are expensive and fickle in mixing and application. These types of wood finishes generally use a catalyzing acid to activate the finish. The catalyst speeds up the cure and recoat times. Most, if not all the two-part finishes require spray setups application as well.
ML Campbell Krystal Conversion Varnish
Some of these finishes are prone to issues, such as clouding, as the finish thickness increases or exposure to moisture. That said they have extremely nice performance characteristics. That makes them attractive especially for cabinet and furniture use. They boast some of the highest solids content of all finishes, ideal for frequently used or high wear/traffic conditions. Other than my days producing high end door and window units I don’t use two part finishes. Thus I have limited experience using two part finishes. In principle the method of finish building is applicable to water-based and two-part finishes. Though I suspect it will need individual tweaking based on their nature and the specific finish used.
No Hassle Types of Wood Finishes – Film Finishes
I like to keep things simple with my finishing process, so the majority of my uses are with shellac, polyurethane, and lacquer (nitrocellulose). Polyurethane and/or varnish differs from shellac and lacquer in that each coat applied forms a distinct layer of finish. Poly tends to impart a yellowing cast on woodwork, though its cheap, easy to apply, fairly easy to repair, and takes well to rubbing out. For the items that I produce it behaves fairly similarly to nitrocellulose lacquer, so I tend to lacquer my higher sheen items as there is less yellowing with the lacquer.
Shellac and lacquer essentially absorb into one homogeneous coat (melt in). That is different from the layering that you get with poly. I used shellac frequently in my early days as I was finishing on the lathe more at that point. It is also very useful as a seal coat if you are doing any refinishing. Its used to seal an item to prevent finish incompatibility. That is, for example, using a water-based finish over previous oil-based finishes. I find it best to mix your own cuts from shellac flakes (super blonde), i.e. dissolving flakes in denatured alcohol. Shellac flakes come in a wide range of tones, so tinting the finish is doable just with the flakes. Since its alcohol based, shellac is also compatible with some dyes as well (transtint for example). Finishing with shellac on the lathe is nice as the continual build of coats develops a French polished effect.
On the use of colorants
Outside of furniture I do not work with any colorants. Meaning dyes, stains, gels, etc., and in those cases my preference for using colorants is to even the natural wood tones. For example, I will use walnut stain or dye on a walnut piece of furniture to even the tonal variation between different boards. Its common to have boards from different trees with tonal differences. So again, if using colorants then the process should be tweaked. Colorants aren’t really my thing as I work with a lot of wood that has natural variation, however as wood turners go there are a lot of turners that use colorants.
Lacquers – that is Nitrocellulose
Deft Brushing Lacquer – Gloss
Polyurethane/Varnish and Lacquers have higher solids contents in the finish compared to shellac. They will form harder surfaces once cured while retaining their rubbing qualities, and this makes them better candidates for developing what I refer to as an ultra-gloss finish. That is a high gloss that has mirror like reflective qualities. I prefer lacquer in this case as it has a lower degree of yellowing that is typical with polyurethane and varnish. I specifically use Deft, made by PPG, as I brush on the lacquer, although I have considered using brushing lacquers from Benjamin-Moore or Sherwin Williams as they may have a higher solids content. So far, I haven’t purchased any of their products to see how they perform. Deft is a nitrocellulose lacquer that has additives to prevent or slow the yellowing over time that nitrocellulose is prone to. Spraying lacquer will also work, though I prefer brushing to control the volatiles in the air and brushing yields thicker coats, thus reducing the total number of coats needed in producing an ultra-gloss. I do spray lacquer occasionally when I do not intend to wet sand or produce a very reflective sheen.
Glue Finishes – do not stick your fingers together
StickFast CA Group
I mention glue finishes mainly for CA, that is cyanoacrylate or super glue. Stickfast, a TMI product, is a good brand. I have toyed with the idea of finishing with CA but have yet to do so. Mainly as it would require a lot of CA to finish my items. There is also the mess that sticks to everything that makes application a bit troublesome.
Despite those issues CA is a topcoat finish for small items. Especially finishing on the lathe. For example, CA is a preferred finish for pen work. Similar to finishing with shellac on the lathe. Building multiple layers is easy as CA dries quickly. Rubbing is done on the lathe. CA also comes in varying viscosities ranging from thin to thick.
Wax on Wax off
Mylands Paste Wax
Waxes are the last category, and on their own they make a poor finish. They don’t fit into this method other than acting as a final protective coat. I also use waxes as rubbing medium for satin and semi-gloss items. I use Mylands paste wax, clear, for all non-ultra-gloss finishes and I use an automotive wax for ultra-gloss finished items. Currently I use the latest Meguiars wax product, as they update their products frequently.