How Does the Finish of an Acoustic Guitar Affect its Tone?

( guest article by Jennifer Hughes of know your instrument.com )

One of the things that people often wonder about when choosing a guitar has to do with the guitar finish. Why is it important and does it affect the tone of the guitar in any way? Acoustic guitars, from entry-level guitars and acoustic guitar models in the $300-$500 range to professional and high-end models, all come with a finish, applied using a variety of techniques.

The finish of the guitar does not only give the guitar an aesthetic appeal and protect it from minor scratches. According to master luthier Dana Bourgeois, it also helps filter unwanted frequencies. Of course, it’s important to choose a finish that would be a good match for the design and voicing of the guitar and apply it so that it damps the frequencies you don’t want. This would allow the acoustic guitar to have improved punch and clarity.

Let’s take a closer look at the different acoustic guitar finishes and just how they affect the tone of the guitar.

Two main types of guitar finish

• Gloss finish - A gloss finish gives the guitar a shiny look and a smooth feel. This type of finish brings out the grain of the wood on the guitar such as mahogany, cedar, spruce or maple.
A gloss finish acts like a sort of lens to let you see the surface of the guitar, especially the wood grain. Some acoustic guitar models are given a high gloss finish and some have a semi-gloss finish. Guitars with a gloss finish are easier to clean - just a quick wip and polish with a soft cloth and you’re done!

• Satin finish - A satin finish gives the guitar a matte look and a bit of a rougher feel. This type of finish does not bring out the wood grain as much as a gloss finish does. A satin finish also tends to wear off with time, leaving some parts that are shiny.

Materials used for the finish

The organic and/or synthetic components of a finish affect its performance. Researchers theorized that the finishes used on Antonio Stradivari’s cellos, violins, guitars and violas contained polysaccharides or sugars. This created a thin and more brittle material that bonded well to the spruce wood while letting the soundboard vibrate freely.

That is just one example. Here are some other more common materials used for acoustic guitar finishes.

• Shellac - commonly used in woodworking. Shellac is non-yellowing and has excellent adhesion. As a guitar finish it’s a good option because it doesn’t dampen the soundboard’s vibrations. It’s easily dissolved in alcohol, making for easy removal and repair.

•  French Polish - mostly used on high-end guitars, applying this is labor-intensive. The French Polish process involves applying multiple coats of shellac in extremely thin layers. The finish needs a lot of care because it’s prone to scratches and is not as durable as other materials. However, this material is said to be the best if you want a great guitar tone as it is thin and allows maximum tonewood response.

•  Lacquer - lacquer creates a tough surface with a glossy sheen. To cure well, it needs a warm and humid environment so the liquid component evaporates, leaving the hardened resin securely bonded to the surface of the acoustic guitar wood.

•  Nitrocellulose lacquer - this is a solvent-based lacquer that contains nitrocellulose. It is more durable than varnishes and is scratch-resistant. This needs to be applied at just the right thinness to prevent cracking. Nitrocellulose finishes can lose their density and shine over decades.

•  Polyester - also durable and scratch-resistant. Polyester also makes an acoustic guitar more resilient to changes in humidity and temperature. It also doesn’t fade into a yellowish hue like some lacquer materials can. Once a polyester finish has completed its curing process, it can be polished to an extremely high gloss and durable finish.

•  Tung oil - Tung oil is a traditional component of wood varnishes. It is a protective finish that cures through the reaction between the oxygen in the air and the large amounts of polyunsaturated fatty acids it contains. It is good at sealing water or moisture out of wood. However, it is not that commonly used for musical instruments because it dampens the vibration of the wood.

What affects the guitar tone?

What really affects the tone of an acoustic guitar is the thickness of the material used for the guitar finish. How well the finish is applied also has an impact on the overall tone of the guitar. When expertly applied at just the right thinness, a finish can make a good guitar sound great.

In general, the thicker the material, the more the sound and resonance will be dampened or choked by the finish. Guitars with a satin finish usually have a thinner coating, but this doesn’t mean that models with a gloss coating sound awful.

Final word

The kind or type of finish a guitar has does not affect its tone significantly. What you need to look for in a guitar is a finish that is applied well and is as thin yet durable as possible. Whether it’s gloss or satin is up to you.