Standard Wood Finishes
Choices, choices, choices. When it comes to applying a new finish to a piece of furniture, that is what you are faced with, choices. While choices can induce an exhilarating sense of freedom and opportunity, they can also create a fog of confusion and uncertainty when there is insufficient knowledge to be confident in the decisions made. We would like to help clear the fog and ensure that your choices concerning the finishing of your furniture are made with confidence. Below we will answer questions concerning protecting wood and enhancing the appearance of wood. So as not to overwhelm you, a second set of finishing options concerning decorative finishes are covered on a separate page.
ENHANCING THE APPEARANCE OF WOOD
We are generally aware that in woods and forests, fallen trees will decompose. Insects, birds and animals, as well as fungi, algae and bacteria, all participate in that process. Two silent partners in the process of decomposition are moisture and sunlight. Either too much water or too little water will weaken wood. Even in a protected household environment, prolonged exposure to high moisture content air, such as damp, misty, winter days or sticky, humid, summer days will help along the process of decay. Extremely dry air will cause shrinkage and cracking. Further, rapid changes from hot to cold, from damp to dry, create stresses which will, over time, weaken wood. Ultra violet light from the sun will damage wood by breaking down the cellular structure of the outer layers of the wood. In our homes the process of decay is usually very slow, even with unprotected wood. However, warping, twisting, shrinking, cracking and and even fading are all evidence that the process is taking place.
Wood Needs Protection
Furniture has been described as functional art. It needs to be useful but we want it also to be beautiful and we further expect it to be durable. In order to preserve our investment in pieces of functional art, we need to protect them from whatever will cause them not to be durable. Most fundamentally, this means we need to protect them from extremes of moisture, rapid changes in moisture and from the harmful effects of sunlight. Hence the craft of furniture finishing.
Two Ways To Protect
Finishing materials used to protect wood from extremes of moisture fall into two categories, finishes which penetrate the wood and finishes which form a coating over the wood. Oils such as tung and linseed have been used as penetrating finishes. (For more information about tung and linseed oil, see our page on restoring oil finishes.) Waxes and various natural resinous materials have been used to form coatings over the wood. Finishes which protect wood from sunlight have almost always included the introduction of earth pigments along with an oil or resin. With the addition of enough pigment, the finish becomes what we call paint.
Protection And Beautification
Preserving wood is an important function of furniture finishes, but since furniture is functional art, creating something which pleases the eye is another demand placed upon furniture finishes. Most often this is done by choosing a finish which will accentuate the natural beauty of the wood. Penetrating finishes do the most to display the natural features of the wood to greatest advantage. However, penetrating finishes are not as durable or as resistant to damage as are finish coatings. External finish coatings also have the advantage of versatility in creating special effects to further intensify the aesthetic appeal of the functional art. Due to concerns regarding the health of the workers who apply these coatings and concerns regarding the purity of our common environment, many of the finishes used historically are no longer legal to apply without a special permit.
Oil: Virtually any oil can be applied to wood and will function at least temporarily as a preservative and perhaps as a beautifier of that item. However, most oils are not satisfactory wood finishes because the oil will either migrate too deeply into the wood and leave the surface dry and vulnerable to wear and weathering, or will not dry out and will leave the surface of the wood feeling tacky. The best oils for wood finishing are tung oil and linseed oil because they will actually harden fairly rapidly at the surface of the wood.
Wax: Various waxes or combinations of waxes have been used to protect and beautify furniture for centuries. Beeswax in particular has been widely used for this purpose because of its abundance. Waxes are not ideal wood finishes however due to their softness, low heat tolerance and low chemical resistance. Hot beverages or alcoholic beverages will both destroy wax coatings. Shellac, lacquers and varnishes have always been preferable to wax, wax has been used only when these other coatings are not available. That said, wax is excellent as a secondary treatment over these other finishes.
Shellac: Shellac is a resin that has been refined from the secretions of tiny bugs that grow in India, Thailand and China. Shellac resins come in a range of colors based on the type of tree the bugs feed upon and on the time of year harvested. There are records of shellac being used as a wood finish as early as the 1500's, but widespread use as a furniture finish did not begin until the early 1800's. Then through the first couple decades of the twentieth century, shellac was the coating of choice for fine furniture.
Varnish or Lacquer: The terms "lacquer" and "varnish" are both used as generic terms referring to any finish which builds a resinous surface layer over the wood to beautify and protect it. Varnish historically referred to finishes that combined one of a number of vegetable oils with one of a number of resins, and a dissolving solvent, usually turpentine. Varnishes formulated with these components have been in use since at least the late Medieval period. Lacquer is generally distinguished from varnish by the fact that it dries quickly and does not include any oils in its formulation. Nitrocellulose lacquer was invented in 1921 and combined a cellulose resin with a combination of fast drying solvents.
For more information on historical coatings, please go to the section of our website covering restoring finishes.
Water Based Protective Coatings
Most of the high end development in the science and technology of furniture finishes is in water based coatings using synthetic resins. These modern water based finishes are harder and are more resistant to chemical damage than the older materials but still have a high degree of clarity and repairability. Non-water based modern finishes have advantages in lower costs, increased hardness or chemical resistance but fail when it comes to worker safety, environmental impact, clarity or repairability. For a comparison table, please see our page on finishes and durability concerns.
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ENHANCING THE APPEARANCE OF WOOD
Revealing The Beauty
Some will contend that the natural colors, patterns and depth of wood surfaces are beautiful in themselves and need no enhancing and further that efforts to enhance actually distract from the natural beauty of the wood. We acknowledge that wood does possess a natural beauty. However, when you look at a standing tree, you don't see any of the beauty of the wood grain within. The sawyer first of all needs to cut the wood of the tree to feature the natural patterns within. Next, a woodworker will take that rough sawn wood and form it into an item of furniture which will show the beautiful grain to fullest advantage. The raw wood however, still does not display the depth, intensity and richness of its own grain pattern. Even simply wetting wood with water will show there is more to be seen than the dry wood reveals. Water evaporates quickly and the beauty it reveals is soon hidden again. Wood finishes not only preserve wood but they create a way of displaying the beauty of the wood in a lasting way. However, even simple oil finishes add a color that is a natural part of the oil itself, not the wood.
Focusing On The Beauty
Hopefully the preceding has illustrated that presenting the beauty of the wood doesn't happen without the careful efforts of a series of craftsmen. A second concept upon which our work as furniture finishers is based is that of "framing." In painting, photography and film making our attention is focused by the artist on a specific scene by placing that scene within a frame. In a similar way, our use of color, sheen and special effects can be seen as a way of framing one's attention on the distinctive features of the wood or on the design of the item of furniture. However, sometimes the wood or the item of furniture is itself a part of the "frame." In such cases the furniture may be finished not so much to stand out on its own as to aid in the creation of a certain feeling or mood in a room. We then become part of an artistic team to create that effect and the natural beauty of the wood is a secondary concern.
At this point we will become very practical and discuss what we do to enhance the appearance of the wood furniture items that come to us for refinishing.
Basic Finishing Process
Once an item has been stripped and any repairs have been completed, we then prepare the wood for finishing. We sand all surfaces with a medium grit of sand paper and then again with a fine grit. The medium grit removes scratches and smoothes the surface, the fine grit does more smoothing to the point the surface will stain evenly and with the right penetration. The piece is then ready to be stained.
Wood stains are formulated from pigments and dyes. Pigments are very finely ground materials, usually derived from mineral sources, some from plant and occasionally from animal sources, that are suspended in a liquid medium to create stains. Pigments are applied to the wood and wiped to force some penetration into the wood fibers and to ensure even distribution of the pigments. As the stain dries, the liquid medium that carries the pigments evaporates and the pigments remain on the wood. Pigments must be sealed in place or they will quickly wear off. Many stain vendors will formulate pigment based stains with a small proportion of a sealing material to hold the stain in place. Dyes can come in either powder or a pre-dissolved liquid form. Dyes are derived primarily from plant sources though also from mineral and animal sources. In contrast to pigments, dyes fully dissolve in the liquid medium and will penetrate wood fibers as deeply as the liquid will. Dyes are absorbed by the wood fibers and will permanently color the wood. Because of the deep penetration and clarity of dyes, dramatic contrasts in grain patterns are accentuated and very vibrant colors can be achieved. Stains are also created by mixing pigments and dyes to create colors and effects otherwise not attainable.
After staining all surfaces are sealed. Stained surfaces must be sealed to stabilize and protect the stain. The sealing of all surfaces, stained or not, is important to minimize the effects of atmospheric moisture. We have seen many pieces come through which have sustained damage due to having only the exterior or visible surfaces sealed. Next, the item is thoroughly sanded with a very fine grit sand paper. We are then ready to begin building up the finish coats of protective coating. Because water based finishes are between 35 and 40% solids, it takes just two to three coats of finish to properly coat an item. Once those coats have been applied, we sometimes use an ultra fine grit sand paper to remove surface nibs.
Those were the basics for applying a standard finish. Very often however there are other steps that need to be taken in order to complete a project which has fully enhanced the appearance of the wood and the forms created by the woodworker. These are listed and defined below:
Two toning: Using a second stain color on certain sections of the item to create interest, highlight features or to make the piece appear more uniform.
Touch up: Repaired defects or damage must sometimes be disguised by creating patterns of wood grain to match the surrounding grain. This is done with the skills and supplies of an artist.
Filling: Sometimes it is preferable to fill the pores of open pored wood such as mahogany, walnut or oak. This gives a smooth, unbroken surface.
Toning: The addition of a small amount of color to one of the finish coats can be used to make the overall appearance of the piece more uniform or can be used to create depth of color.
Shading: The addition of a slightly larger amount of a deeper color to the finish can be used to create a semi-transparent shadow effect, typically around the perimeter of a table top or at certain focal features of the piece.
Highlighting: A heavily pigmented paste material is used to wipe across highly carved or figured elements depositing the paste in the recesses to accentuate the relief.
Glazing: A slightly thinned version of the paste used to highlight can be used on flat surfaces to vary the color or the intensity of color.
In-painting: Certain styles of furniture were designed with sections painted with a contrasting color, usually black. This is often seen in furniture from the 1920s.
Distressing: Wood surfaces can be artificially aged or damaged. Sanding through finished edges, adding specks and squiggles, denting with nail tips and creating scratches are some of the techniques used to distress.
Crackle or Craze: Many older finishes will show age by crackling or crazing. This effect can be replicated with clear finishes if desired.
Polishing: Certain sheens of finish are obtained by sanding with micro grained sand paper and then by polishing with compounds and perhaps buffing with a wool pad.
Options For Surface Sheen
The final consideration in finishing is the decision as to the sheen of finish. Finish sheens are measured by the amount of light they reflect, 100 being 100% light reflection and 10 being 10% light reflection. Gloss finishes are typically in the 80-90% range, Semi-Gloss finishes are above 50%, Satin finishes are below 50%, flat or matte are down below 25%, dead flat finishes are below 10%. Lower sheen finishes are made by mixing additives to the finish which reduce the ability of light to pass through the finish. One concern people commonly have about lower sheen finishes is their durability and clean-ability. Unlike some house paints, there is no reduction in either durability or clean ability with lower sheen water based wood finishes.
Finishes Change Over Time
People refinishing older furniture will often ask for a satin finish, thinking a satin finish would most accurately represent the finish originally on a piece. The reality is that all surface coated finishes tend to move toward the middle of the scale of reflectivity over time. Shellac finishes are very glossy by nature. Old varnishes were not quite as glossy as shellac but were also fairly glossy. As these naturally shiny finishes wear, fine scuffs and scratches break up the reflectivity of light and the sheen lowers. Also, one impact of ultra violet light is to create microscopic crazing within the finish which also impedes light transfer. Oxidation will cause chemical changes which darken the finish and also lower sheen. On the other hand, the additives which lower the sheen of finishes tend to accumulate at the top of the finish layer. The natural scuffing that comes with use will reveal the shinier material underneath the flatting additive and the finish will begin to appear more glossy. Consequently, all surface coated finishes over time will tend toward a more satiny appearance. In contrast to surface coated finishes, oiled finishes start out medium to low in sheen and become lower with wear. For more information on different types of finishes, we would again encourage you to view our pages which deal with restoring finishes.
How Shiny Should The Surface Be?
Are there rules of thumb for what sheen should be used on a given piece of furniture? Sort of, but there are no hard rules. In general, higher sheen is used on more formal pieces and on pieces with more red in them. The most sure rule is however, what looks good to you is what you will most enjoy seeing for the years you and that furniture item share a home.
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