Wood Finishing Techniques

The craft and skills of the furniture maker for long has been passed from master to apprentice and so have the methods of finishing their work. Early woodworkers employed commonly available materials to protect the wood furniture they made.
The beauty of solid wood is in the finish. The finish will seal the wood stabilizing the structure and protecting it from the elements. The finish is the final transformation of the wood.

Shou-sugi-ban, a Japanese method for preserving wood through fire originated in the 18th century. First the wood is burned, charring he surface. After the wood is coated with a natural oil. Traditionally Japanese cedar (cryptomeria japonica) wood was used because of its ability to withstand a deep burn and resist rot and repel water.

In the early days of furniture manufacturing oils and waxes were used to varnish the wood and preserve the appearance of the final piece. These were followed by shellac which lasts much longer than the oil or wax. Unfortunately, shellac is not waterproof. Currently there are many forms of lacquer being used in finishing wood furniture. Today we have NC lacquer or nitrocellulose lacquer. NC lacquer is inexpensive, blends well with pigments and dyes, and dries fast it is the most widely used finish today.

NC lacquers began to be produced following the America’s Civil War. Post war gun cotton stockpiles were a safety hazard. Cellulose nitrate is created in much the same way as TNT. Chemists sought a new use for this flammable substance. Camphor was found to make an excellent solvent for the cellulose nitrate and the modern NC lacquer was created. Although it was never as explosive as TNT early NC lacquers were extremely volatile. These same films were used in the early motion picture industry. Projection booths were fireproofed because of the explosive nature of the films they were recorded onto. Decades would pass before this finish was stabilized and its volatility diminished.

Solids dissolved in solvents define the broad groups of liquids and the pigments that are mixed together to convey color onto the wood. The finish maybe poured, wiped, brushed, rubbed or sprayed onto the wood surface. The porous nature of natural wood allows the absorption of the finish into the structure revealing the intricacy in the patterns of the grain.
These finishes cure or dry in different ways. Some finishes employ the evaporation process. These finishes dry and harden through the evaporation of the solvent. The pigments will become a hard-solid film when the solvent is removed. Lacquer and shellac rely entirely on evaporation to dry.

Next, we have the reactive finishes. This type of finish cures by means of a chemical reaction after the thinner evaporate. The reaction is created by the absorption of oxygen or by a second chemical agent called a catalyst.
Finally, we have the coalescing finishes, or common water-based finishes. These finishes dry by both the solvent evaporation and a chemical reaction. These finishes are easy to clean, have low VOC’s and can be recoated in a couple of hours. Water catalyzed polyurethane, latex paint are examples of these kinds of finishes.

Today, at A-America, we use catalyzed lacquers. Catalyzed lacquers dry by evaporation much in the same way as conventional lacquers, but then is cured by a reaction initiated by a catalyst. When these finishes dry, they are food safe and highly resistant to damage from most food items and alcohol. These lacquers flow and work well with stains, glazes, toners and colorants in the finish. Catalyzed lacquers offer enhanced moisture protection.
The complete finish may be composed of a few layers of stain and lacquer or ten or more different layers to create the color and dimension in the final piece.

Below you will find a glossary of terminology used

Acrylic Lacquers, Aniline (Acid) Dyes, Binder,Bleaching, Blushing, Catalyst, Catalyzed Lacquer, Catalyzed Vinyl, Conversion Varnish, Coat, Danish Oil, Distressing, French Polish, Glazing, Gloss, Metamerism, Mirrored Polish Finish, NGR Stains, Orange Peel, Over Spray, Penetrating Dyes, Penetrating Oil, Penetrating Oil Stains, Pickling, Pigmented Oil Stains, Polyester, Sealers, Shading, Shellac, Solvent, Staining, Standard Lacquer, Toners, Varnish, Vinyl Lacquers, Wash Coats, Water-Based Stains and Wiping Stains

Acrylic Lacquers

A clear hard and high-quality finish for furniture and a variety of wooden products. Acrylic lacquers use a synthetic polymer, acrylic resin.
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Aniline (Acid) Dyes

Before pigmented stains began to be manufactured in the 1950’s most wood coloring was done using dyes. Discovered by accident in the mid 19th century with aniline, a clear poisonous.
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It binds the pigment particles together so that they stay on the surface and forms a solid film becoming the glue that holds the pigment onto the wood.
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The chemical process used to remove color or whiten solid wood. This process may be used to lighten an extremely dark wood or to whiten a lighter colored wood. Most woods do not turn completely white when bleached.
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The whitish, cloudlike haze that occurs in fast-drying finishes, especially lacquer, when they are sprayed in very humid conditions. Blushing is most often due to moisture (water vapor) trapped in the film or to bits of resin precipitating out of solution.
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Chemically, an ingredient added to a product to provide additional performance characteristics, such as faster drying, chemical resistance, or increased hardness of the finish.
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Catalyzed Lacquer

A modified nitrocellulose-based coating with a catalyst added for enhanced performance.
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Catalyzed Vinyl

A catalyzed coating with a vinyl resin base. Extremely tough and resistant to most chemicals.
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Conversion Varnish

A catalyzed alkyd-based coating that is tough and resistant to household chemicals.
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The final protective film of a finish system. There are various top coats with different properties.
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Danish Oil

The general name for any number of wipe-on coatings based on tung or linseed oil, with solvents and resins added to enhance both drying and performance.
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May be either of a mechanical or chemical nature to give special effects. *Filler: Used to advance the final build and smoothness of the finish. Filler may be neutral or a contrasting color to accent the pores. The use of filler alone may not completely fill all pores and is generally limited to horizontal surfaces of ring-porous woods such as elm, oak and ash. Close Grain species such as cherry, maple, birch and poplar seldom require filler. Few vertical surfaces benefit from the added labor of a filled finish.
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French Polish

A mixture of shellac and alcohol rubbed on with a cloth pad, usually to a high sheen.
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An added step for achieving color uniformity and depth, and for highlighting the wood’s grain pattern. It also is used for tortoise shell, marble effect, or antiquing.
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Also referred to as sheen, a surface shininess or luster. *Hand-Rubbed Finish: The name given to an effect that is created by the manual process of applying a combination of abrasives and lubricants, after the final topcoat has dried, to smooth, flatten or dull that topcoat.
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A phenomenon that occurs when two colors appear to match under the same or similar lighting conditions.
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Mirrored Polish Finish

Requires several steps of wet sanding, mechanical buffing, and polishing.
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NGR Stains

Non-grain-raising (NGR) stains are dye solutions that do not contain pigments. Spray application gives an overall transparent color to the wood, offering a high degree of clarity. Some fading may occur over time.
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The description of a coating which does not flow out smoothly; exhibiting the texture of an orange.
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SOver Spray

The dry, pebble-like surface caused when sprayed finish begins to dry in the air before it hits the surface.
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Penetrating Dyes

Deep color, fast-drying stains often carried in solvents as a liquid or as a gel. Some water-soluble versions are available.
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Penetrating Oil

An oil-based material designed to penetrate into the wood. It usually requires reapplication from time to time.
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Penetrating Oil Stains

Almost always a thin liquid mixture of oil and thinner with a dye added for color.
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A white or light-colored pigment in either an oil or water vehicle. When wiped or brushed on to an open pore wood, the white stays in the pores and is usually wiped off the surface, either entirely or partially depending on the effect desired. Similar to the application of Filler.
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Pigmented Oil Stains

Almost always an oil-based liquid with pigments (not dyes) added.
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A very high-solids-content coating consisting of two components that require special care in handling and spraying. Leaves a deep, wet-looking, clear or colored finish. Limited repair-ability. Polyurethane: Usually a two-component system that may have a higher solids content than lacquers. Takes somewhat longer to dry than lacquer. A highly durable finish which, as a result, is very difficult to repair.
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Compounds that provide a sand able coating and a smooth surface for final topcoat application, provide system toughness and holdout, provide moisture resistance, and contribute to build and clarity.
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A technique that can be used to either highlight contrast or create a more uniform appearance.
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A wood finish extracted from the secretions of an Asian insect; fast-drying and usually waxed for additional protection.
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A substance in which another substance is dissolved, forming a solution. Finish solvents include paint and lacquer thinner, mineral spirits, gum turpentine and denatured alcohol.
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One of the optional operations in wood finishing, producing the desired undertone color and complementing the wood with proper distribution of color, depth of color and clarity of grain. Selection of type of stain used is governed by desired aesthetic result.
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Standard Lacquer

A nitrocellulose-based coating, usually without any additives, that dries by solvent evaporation. Generally easy to repair.
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Transparent or semitransparent colors used to even the tone of wood.
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An oil-based finish used to coat a surface with a hard, glossy film.
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Vinyl Lacquers

Catalyzed lacquers made with a vinyl resin rather than a nitrocellulose base.
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Wash Coats

Thin solutions applied as a barrier coat to wood. They are used prior to wiping stains for color uniformity. Shellac wash coats help finish materials adhere to resin-secreting woods.
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Water-Based Stains

Are made by adding hot water to universal tinting colors, then diluting that solution to the desired strength with cold water. They provide good grain clarity but raise the grain and are slow to dry.
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Wiping Stains

Thin pastes or thick liquids with pigment suspended in a solvent vehicle; applied and wiped with a cloth to remove excess stain.
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