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FINISHING OPTIONS FOR MUSICAL INSTRUMENTS
Overview
There are many design, process and material choices to make when creating a musical instrument. One of the most perplexing for the inexperienced builder is choosing the finish. In an effort to help with this selection we present an overview of the finishes most often used on musical instruments - explaining the distinguishing characteristics, general application process, and compatible products for each. Following these general product descriptions these finishes will be compared to help narrow your choice to the most appropriate finish for your needs and shop situation. And finally, in articles separate from this overview - accessible from the drop-down box in the upper left of this page, we provide detailed instructions for the application of five finishing products.
The materials that are used as musical instrument finishes vary greatly in their properties and application. Almost all of them were developed originally for general woodworking or furniture finishing and were later adopted as musical instrument finishes. For hundreds of years, basic oils and simple varnishes have been used as the protective coating for musical instruments, wooden furniture, and other wood products. Nitrocellulose lacquer, however, has been the primary wood finishing material, and American guitar factory preference, for over eighty years. More recently polyurethane, polyester, and other catalyzed coatings have been used in guitar manufacturing and the quality of water-based finishes has increased steadily so that now the best of them equal or exceed the quality of nitrocellulose finishes . The more exotic synthetic or catalyzed finishes are best suited to factory situations, not to the average small-scale guitar maker.
From all of these possible finishing several are most useful and appropriate to individual hand-makers and smaller production shops: 1) water-based lacquers, 2) solvent-based nitrocellulose lacquer,3) shellac for French polishing, and 4) an easy-to-use wipe-on oil varnish.
The following general product descriptions can be used to compare the physical properties, methods of application, and the strengths and weaknesses of each of these products.
WATER-BASED LACQUER
With personal health and environmental concerns (and regulations) growing steadily over the last twenty years, the manufacturers of finishing materials have seen that the long-term trend is moving away from solvent-based finishes and toward less-hazardous, less-toxic products. In response, many manufacturers set the goal to manufacture a lacquer with all of the positive characteristics of current solvent-based lacquers but without the hazardous, toxic solvent base.
For more than fifteen years now there has been steady development of many types of water-based lacquers intended to eventually replace the solvent-based product for all applications. There have been hits and misses during this time, but the currently available water-based lacquers are finally close enough to this goal to be useful as guitar finishes. These products are now as easy to apply and work with as solvent-based lacquers but now give great acceptable results - especially considering the obvious advantages of using a less-toxic water-based system. Guitar builders using these products claim that they are achieving finishes that are comparable with those of the solvent-based product.
As with the solvent-based lacquer system, there are many good products available for pore filling, color shading, sanding, and buffing that are compatible with this water-based lacquer. Although most builders are spraying the water-based lacquer, this product also works well as a brush-on finish.
The advantages of using this water-based lacquer are tremendous for all woodworkers. The health risks and environmental harm are diminished to almost nothing. Clean-up is easy with warm water. The vapors are not harmful or toxic so no breathing protection or strong ventilation is required. The water-based lacquer has very high solid content so less material is used to finish each instrument, and there is no need for lacquer thinner during spraying or clean-up. Any required thinning is accomplished with distilled water or a compatible reducer. This makes the water-based system far more economical (guitars per gallon) than using solvent-based lacquer. Because of its less-toxic nature it can also be shipped without restriction -unlike hazardous/toxic materials.
We presently offer the KTM9 waterbased finish and are confident that it is the first and only waterbased finish to complete with nitrocellulose lacquers. It is clear, hard, repairable, economical, does not require a cross-linker or other additives and shows not blue tint on the finished instrument. It is the finish that we recommend most highly to beginning and professional luthiers.
Other materials used with water-based lacquer:
Ÿ Staining raw wood - Use either our Alcohol Soluble Aniline Dyes, FSB or Water Soluble Aniline Dyes, FSBW or dye concentrate, FMDY (Water-Soluble or MEK-Soluble).
Ÿ Shading color mixed into finish - Use either Water Soluble Aniline Dyes, FSBW or Water Soluble dye concentrate , FMDYWF.
Ÿ Pore filler - LMI Micro-bead Acrylic Paste Filler works fine but for best results, use our System 3 clear epoxy filler ( FSB1.5K or FCC1.5K) with the silica thickener (FST1Q)
Ÿ Sealer –Use the finish itself as a sealer or one of our shellacs.
SOLVENT-BASED NITROCELLULOSE LACQUER
This finish material has been the dominant finish used by U.S. musical instrument factories for steel string guitars, arch top guitars, banjos and mandolins since the 1920’s. It would not be an exaggeration to say that all, or nearly all, vintage/collectable American factory steel string instruments are finished in lacquer. (Until very recently solvent-based nitrocellulose lacquer was simply referred to as “lacquer” in the musical instrument business.)
This finishing material is made of nitrocellulose combined with other resins (to promote flexibility, durability, etc.) dissolved in lacquer thinner solvent. The lacquer film forms and cures as the solvent evaporates. Lacquer thinner is a volatile, “hot”, solvent containing a combination of hydrocarbon and chemical solvents - including naphtha, xylene, toluene, acetone, various ketones, and others. This strong solvent base is lacquer’s best advantage and primary disadvantage.
Lacquer thinner solvent is strong enough to dissolve subsequent coatings together, and it can easily dissolve a cured lacquer finish as well. This feature makes the finishing process and any touch-up or repair easier and more controllable compared to other finishing systems (with the possible exception of the KTM9 waterbased finish). Solvent-based lacquer has been so extensively used in the guitar and furniture industries that all of its application and cured film properties are very well known and available. The resulting cured lacquer film is excellent for musical instruments. It is hard and durable, yet flexible, and can easily be buffed to a beautiful high gloss when cured. This finishing system is also well supported with a full spectrum of pigments and dyes for coloring, as well as abundant pore filling, sealing, spraying, sanding and buffing products (see our catalog listings).
Although nitrocellulose lacquer can be applied by brush (with the addition of retarder ), it is best applied, as intended, with proper spray equipment and some kind of ventilation hood or booth.
The main drawback of lacquer thinner solvent based finishing is the hazardous nature of the evaporating solvent itself. Intermittent exposure to the lacquer thinner vapors is a potential health risk, so it is necessary to wear a vapor mask, and to avoid skin and eye contact as well, when working with lacquer or lacquer thinner. Strong ventilation of the spray mist while spraying, and of the curing instrument after spraying, is a must. While most guitar builders prepare for, or accept, the space, equipment and safety requirements needed to spray lacquer effectively, there is a small but growing number of amateurs and professionals working to eliminate hazardous and toxic materials from their homes and shops. For these builders solvent-based lacquer is problematic.
LMI supplies Lawrence McFadden™ solvent-based lacquer (our part FL128). This McFadden™ lacquer is the most widely used and respected nitrocellulose lacquer product line available for musical instrument finishing. This finish was specifically developed for guitar finishing and is now used by many high-end production and repair facilities. To complement the finish lacquer we offer McFadden’s matching sealer (FLSW) and lacquer retarder (FLRFT).
Other materials used with solvent-based lacquer:
Ÿ Staining raw wood - Use either our Alcohol Soluble Aniline Dyes, FSB or Water Soluble Aniline Dyes, FSBW or dye concentrate, FMDY (Water-Soluble or MEK-Soluble).
Ÿ Shading color mixed into finish - Use either our Alcohol Soluble Aniline Dyes, FSB or dye concentrate - MEK-Soluble, FMDYMEK.
Ÿ Sealer used under lacquer - Use our McFadden Vinyl Sealer, FLSW or Shellac/alcohol solution.
Ÿ Pore filler - Use either our McFadden's Pore Filler, FPF or LMI Micro-bead Acrylic Paste Filler, FMBF.
FRENCH POLISHED SHELLAC
French polishing is a method of applying finish to wood by hand with a cotton pad. In the guitar world the term "French polish" is understood to be a shellac spirit varnish that has been applied by the French polishing method. Most of the fine old musical instruments made in Europe were French polished, as are a majority of fine classical guitars being hand made today. It is a most highly-prized and desired finish for both its visual and tone enhancing characteristics. The luster, texture and color of the wood are all noticeably enhanced under an expertly applied French polish finish. The cured shellac film is also very thin and flexible and is believed to produce the clearest and most natural sound from the vibrating wood of the guitar, especially the top plate.
Even though the French polishing application method is very simple with minimal material and equipment requirements, achieving a professional quality finish is highly dependent on the practiced skill and experience of the finisher. The only materials required are shellac, alcohol, lubricating oil, fine pumice, and a special polishing pad. This polishing pad is made of a small wad of cotton or wool wrapped tightly inside a linen cloth that is held firmly in the palm of the hand during polishing. This polishing pad, lightly charged with the shellac solution, is wiped (“padded”) in a continuous motion over the wood surface with each pass leaving a very, very thin layer of shellac over the last. Multiple polishing sessions are required over many days or weeks to achieve the best results.
Even though applying shellac by this method is very labor intensive and time consuming, most finishers seem to receive enough personal satisfaction from the resulting finish to warrant the effort. The French polishing method will be explained in more detail in a following section.
The recipes for shellac spirit varnish are many, but the most basic formula is shellac (Lac button or flake) dissolved in denatured alcohol solvent. Some other recipes may contain small amounts of common gums or resins intended to improve the resulting film in some slight way, but most finishers use the basic shellac/alcohol solution. The finish dries to the touch almost immediately because of the fast evaporating alcohol solvent but it takes weeks or months for it to fully cure.
The advantages of using French polish as a guitar finish are related to both the finish and the process. The beauty of the wood under this finish is undisputed, and it is generally regarded as the best finish for tone. Even with these accolades for the finish, the actual process, French polishing, has benefits for the maker. It is very “organic”, very personal and tactile. The finisher can watch the surface closely as he works and can minutely adjust material and method as the finish slowly builds and improves through multiple polishing sessions. This direct connection to and control of the results will certainly appeal to many craftsman. There is no equipment required, the materials are few and inexpensive, and the finishing can be done in a very limited space. The vapor and material are not hazardous or toxic, no need for air ventilation or face mask. This finish can easily be repaired or refreshed at any time. Additionally, shellac is used as a sealer or initial wash coat under any finish.
Although this list of advantages seems to make this the overwhelming choice for any instrument or situation, here are some drawbacks to consider. Even though a French polish finish is thin and flexible (good for sound) it is not very protective against even minor physical abuse. It will dent, scratch, or wear away in situations that would not affect the much harder lacquer finishes. This padded shellac finish is protective enough for classical guitars that are usually handled very carefully but not at all suited to instruments that may be handled more casually like electric or steel string guitars. To achieve an acceptable finish by French polishing requires the development of skills that are entirely new and different to most woodworkers. This works against the success of the novice builder when finishing his first instruments. The overall time and intense hand work required for French polishing limits its use in the smaller shops with higher production as well. In both of these cases spraying or brushing of some lacquer product may be more appropriate.
LMI provides all the necessary materials for French Polishing together in the Finish section. You will find three grades of shellac flakes available - blonde (pale), amber, darker amber. Some builders prefer some degree of amber shade in the finish and one of these three grades will suit their needs. Also offered in this section are denatured alcohol solvent (FPDENAL), pumice for filling/leveling (FPPUM), and rottenstone (FPROT) and felt pads (FPFELT) for rubbing out the finish. The pad lubricating oil (olive oil, paraffin oil, or mineral oil) and the cotton or linen cloth to make the pad are readily available in markets and thrift stores.
OIL FINISH
Most oils available as wood finishes are either linseed oil or tung oil in some form, with or without any additives. Some of these oils are thinned with mineral spirits to make application easier. These oil finishes are actually varnishes because they are reactive finishes - meaning that they change into a hard film by exposure to air (oxygen) not by the evaporation of the solvent like lacquer or shellac. These oil varnishes are probably the earliest and simplest wood finishes and the natural luster, or glow, of wood under an oil finish is very appealing.
Of all the oil varnishes available for use as a simple wipe-on finish for musical instruments we offer and support the use of the Tru-Oil product line. Tru-Oil is a polymerized linseed oil with other natural oils added. This formulation will actually build-up as a finish unlike the raw or boiled linseed oils. The Tru-Oil wipe-on varnish (our part FTO) and its matching Sealer-Filler (FTOS) have been used for years to finish hardwood gun stocks so its properties and application process are well known. This product is very easy to use and produces a hard, thin and flexible finish. Although it is not as protective and durable as a lacquer finish it is quite acceptable as a guitar finish.
The real strength of this oil finish is that it is extraordinarily easy and safe to use - very user-friendly. No equipment or ventilation or mask are required. Only a clean cloth is needed for application. It takes little or no skill to achieve an impressive satin sheen finish on wood. This wipe-on oil is ideal for the novice guitar maker with limited finishing experience. With an initial pore filling process the finish can be made as smooth and flat as a factory lacquer finish, or multiple thin coats can be applied directly to the raw wood for a very natural open pore finish. Both ways have been successfully used on acoustic and electric guitars, and some commercial electric guitar manufacturers use oil varnish for necks and/or bodies on some models. Oiled necks have a faster, more natural feel than lacquered ones.
The application of the oil itself is incredibly simple. Just wipe the oil over the surface with a cloth, then wipe off any excess material with a fresh cloth or paper towel to leave a very thin coating. This thin coat will harden in several hours and the next coat can be applied over the last. Five or six, or more, coats are applied over several days to achieve the depth or thickness that is desired. The finish can be polished and waxed, or left as is when the last coat dries.
Although the Sealer-Filler (FTOS) is intended to fill the surface before the oil coats, it is advisable to seal the surface first with shellac whether the pores are to be filled or not. Either of our two pore fillers (FBF or FMBF) can also be used under the Tru-Oil wipe-on varnish.
GUIDE TO SELECTING THE BEST FINISH FOR YOUR SITUATION
We hope the previous descriptions of our finishing materials have helped you decide on the best one for you. Each of these finishes can produce a good sounding musical instrument, so your choice may be driven more by your shop situation and the expectations for the type of instrument that you are finishing. Even with that said you will have several alternatives that will accommodate your situation or needs. The following observations may help narrow your choice further.
Ÿ If you intend to make steel string guitars for the commercial guitar market you will most likely need to use the tried and true solvent-based nitrocellulose lacquer system used on most other commercially available guitars. This, of course, requires a complete spray booth, compressor, spray guns, safety equipment, etc., and the space and resources for this equipment. The expectations of most store buyers are conservative and these buyers will usually not take a chance on guitars that are very different from the established brands.
Ÿ If you are making steel string or electric guitars and have spray equipment but want to avoid the use of hazardous materials water-based lacquer is your best choice. When it is expertly applied it is as hard and durable as the solvent-based product and can be virtually indistinguishable from it. A spray booth is useful but not required if the spraying is done in an open area with mild ventilation. Even some very experienced guitar makers with complete spray facilities and years of experience with the solvent-based lacquers are beginning to work in the water-based lacquers.
Ÿ If you are finishing a steel string or electric guitar without spray equipment your best choice is to apply the water-based lacquer by brush. This is slightly more labor intensive and time consuming than spraying but with careful brushing and sanding between coats the results can be the same as with the sprayed finishes. The resulting finish will be durable and glossy as expected on these guitars and, of course, you will also have the benefit of working in a less-hazardous, less-toxic environment.
Ÿ If you plan to develop a full service guitar repair facility you will need be able to spray solvent-based nitrocellulose lacquer because most of the acoustic and electric guitars you'll see for repair are finished with it. French polishing is also very useful for most minor touch-ups on any finish.
Ÿ If you are making a classical guitar and already have spray equipment you may apply either the solvent-based lacquer or the water-based lacquer. Although French polished shellac is held in higher esteem for classical guitars, many makers around the world have been very successful with these harder finishes. It is common practice now by many makers to finish the sides, back, and neck in a more durable finish and only French polish the top plate - getting the best from each finish. Those makers concerned with the hazardous and toxic nature of the solvent-based lacquer will use the water-based system.
Ÿ If you are making a classical guitar in the most traditional manner then French polishing is your only choice. Learning to professionally French polish requires patience, time, and serious attention and concentration to the process, but the same is true for traditional hand-bending of the sides, hand-planing and scraping of the plates, and hand-making of the mosaic rosettes. Mastering these and other traditional hand skills will take consistent practice and commitment.
Ÿ If you are working with minimal equipment and working space (possibly a small area or table in your home) your instrument can be effectively finished by either brushing water-based lacquer, French polishing shellac, or wiping on Tru-Oil varnish. Each of these finishes is non-hazardous and can be safely applied in your home with no more equipment than brushes or cotton cloths. The oil is the absolute easiest to apply, brushing the water-based lacquer is slightly more involved, and the French polishing requires the most practice and skill. The resulting instrument finish from any one of these materials can range from merely adequate to true professional level depending on your experience and skill.