by Arnold Schnitzer
This Article Was Originally Published On: April 15th, 2016 #Issue 18.
“Varnish” is a word that is used to represent any non-opaque substance that is used on the surface of wood to protect it and enhance its appearance. Its protective property is a result of a tough and rigid film that forms when the applied material cures. This dried film protects the wood from dirt, smoke and pollution, abrasion and minor bumps. A fine varnish is nearly transparent, enhancing and allowing the figure and grain in the wood underneath to show through, while imparting a pleasing color to the instrument.
To be clear, an oil finish that is applied to bare wood and then soaks in and dries is not technically a varnish, because it does not leave a film on top of the wood. Oil finishes – such as WATCO® (Danish oil), tung or linseed – applied directly to the bare wood are frowned upon by makers of basses and other violin-family instruments. Finishes like these that soak in deeply can affect the vibrational characteristics of the wood, and they just don’t have the right look for string instruments.
There are four types of varnish used regularly on string instruments: oil varnish; spirit varnish; lacquer; and conversion varnish, such as polyester and epoxy. Lacquer and conversion varnishes are generally used only on factory-made instruments of lower quality and price. They can be applied quickly by spraying, and are well-suited to a fast-paced factory environment, as they can often be applied start-to-finish in a single day. Conversion varnishes are usually quite thick and heavy, and not well-suited, tonally, to fine acoustic instruments. As a colleague once said, “You don’t want to run a footrace in a raincoat.” Lacquer (nitrocellulose), made from a relative of the explosive nitroglycerin, can be applied quite thinly, and can be very beautiful, but is iffy for bass, because it tends to be inflexible, causing it to crack and craze on large surfaces subject to seasonal wood movement. Another disadvantage to lacquer is that it must be applied in an explosion-proof spray booth, because it has a tendency to go “BOOM!” like its cousin.
Spirit and oil varnishes are the finishes of choice for better violin-family instruments. Spirit varnish is based on shellac and other resins dissolved in alcohol; oil varnish is usually a linseed or walnut drying oil base into which other resins and solvents are cooked. Spirit varnishes dry very quickly and can be difficult to apply by brush, requiring skill and experience. Oil varnishes dry slowly and require sun or artificial light, and/or the addition of special additives, to properly cure. Either type of varnish has to be applied in multiple coats, with adequate drying time and some prep work between coats. The color of the varnish on a violin-family instrument is mostly in the film, and not in the wood. Either the varnish itself has inherent color, or pigments are added to it. There are many methods of applying oil varnish: brushing, wiping, rubbing on with the hands, and occasionally, spraying. Spirit varnish is applied by brushing or spraying. Some makers apply pigments, or glazes, between coats of varnish, usually by wiping or stippling with a pad. Typically, a spirit varnish can be completed in 3-7 days, while an oil varnish will usually take a week to a month, sometimes more.
The varnishing process begins with prepping the wood. Commercial instruments are prepped mostly by sanding; finer ones are prepped primarily using scrapers, thin steel blades of various shapes, which are pulled across the wood, producing very fine shavings and a subtly textured surface. Some makers prep with an ancient plant-based abrasive called “horsetail.” At this stage, many makers “suntan” their instruments using ultraviolet lights or sunlight. It is not practical for bass makers to tan their instruments in the sun, because of their size, and the fact that strong, hot sunlight can cause damage, such as cracks and seam openings.
After prepping, a single or multiple-step process is used to apply a ground to the wood. Makers disagree on exactly what the term “ground” means, but it’s generally accepted to be the base color sealed in place, sometimes with dissolved minerals. On most instruments, this ground is a golden-brown color. Fine instruments have a multi-chromatic appearance; various colors and shades are seen from different angles, with the ground color visible through the outer layers. When done well, the varnish seems to glow from beneath.
When the ground is dry, the varnish color coats are applied. The final coats are usually clear, to protect the color coats below. Then, the instrument must rest for a while, so the varnish can harden as the solvents dissipate. After this stage, the maker may rub the varnish with progressively finer abrasives, such as pumice and rottenstone mixed with oil, polishing compounds, or modern super-fine papers, to achieve the desired gloss level. Some makers prefer the look and feel of bare varnish that has not been rubbed-out. Others “French-polish” the varnish by vigorously rubbing with a pad charged with alcohol and resin (usually shellac or sandarac).
Here are some frequently asked questions and answers about varnish relevant to basses:
“Which is better, oil or spirit?”
The ancient Italian master instruments were finished with oil varnishes. Some makers, including me, believe that a properly formulated and applied oil varnish is more permanent and protective. However, spirit varnish can be extremely transparent and is available in a range of colors. Several quality makers use it exclusively, because it is fast-drying and beautiful. Unfortunately, spirit varnishes are not very water resistant and may dissolve if an alcoholic drink is spilled on the surface.
“Does varnish effect the sound?”
Yes. An overly thick varnish coat can choke the sound of a bass. I’m not sure if anyone could tell the difference between identical basses finished in spirit vs. oil, providing the film is of similar thickness. As mentioned above, conversion varnishes are usually quite thick and not the best choice for tone.
“Is it okay to refinish a bass?”
Depends. A vintage or antique bass will usually suffer devaluation if the varnish is disturbed. And the tone may be affected. A student bass may actually be improved with a good re-varnish. Touching-up varnish should be done by a skilled luthier.
“Why aren’t basses finished on the inside?”
Good question! One would think that finishing the inside surfaces would help reduce the variation in the wood’s moisture content, and make the instrument less susceptible to weather damage. But the aging and maturing of string instruments occurs partly due to repetitive climate changes and drying of the wood from the inside out. Also, when a crack occurs, cleats are usually glued across the crack on the inside of a bass. A finish on the inside would prevent the adhesion of these cleats.
“What is an ‘antiqued’ varnish?”
Some instrument makers take extra steps to make their instruments look old and worn. The techniques used include shading, distressing, partial varnish removal, abrading edges, and adding “dirt” to corners and areas that typically get dirty over time. Antiquing can be done with a true artist’s skill and eye, but can also be rather unconvincing. The practice is commonplace, but somewhat controversial in the string instrument community.
“How should I care for the finish on my instrument?”
The most important thing is to keep it clean. Wipe off rosin immediately after bowing sessions, using a microfiber or cotton cloth. Once in a while, mist a little clean water on a soft rag and wipe the instrument down to remove dust and dirt. Occasionally, you may want to shine it up with a polish that does not contain silicones. Be careful not to get any polish into open cracks or seams, as this could prevent glue from adhering where it’s needed in the future.