Fig. 1. Changes in temperature and humidity can cause checking in traditional nitrocellulose lacquer finishes.

So far, we’ve explored ways to clean and condition your guitar with an emphasis on the fretboard, bridge, and hardware [“The Great Guitar Cleanup,” December 2013]. We touched on caring for the finish, but this subject warrants further discussion.

Over time, sweat, dirt, and oils build up on the guitar’s finish and slowly break it down. This causes the finish to develop a hazy film and become discolored. In addition, if your sweat has a high acid content (low PH balance), it can actually cause the finish to deteriorate, especially where you rest your arm. Sweat contains water, acids, salt, and several minerals that are corrosive to finishes and hardware. When you add in environmental issues, such as dust and pollen, it’s no wonder our guitars get so filthy.

A little background. There are many different types of finishes used on stringed instruments. Vintage instruments typically sport nitrocellulose lacquer—a thin, hard finish that lets the wood resonate well. But nitro is also prone to checking and cracking over time (Fig. 1), especially when the instrument is exposed to sudden temperature and humidity changes. To combat this, many modern guitar builders and manufacturers cover their instruments with finishes that are more impervious to environmental conditions. These include urethane, acrylic, polyester, and epoxy formulations. In some cases, the switch from nitro is a way to save production costs, but builders can also be motivated by a desire to spray materials that are less harmful to the planet and workers. For example, in recent years there has been a trend toward UV-cured and water-based finishes, both of which reduce chemicals released into the atmosphere during production.

Fig. 2. A gloss finish (left) looks shiny and usually feels smooth and glass-like to the touch. Fig. 3. A satin finish (right) has a softer, less reflective sheen, allowing you to often feel the wood grain.

Modern finishes come in two styles: gloss and satin. Gloss finishes are shiny and have a glass-like look (Fig. 2), while satin finishes have a softer, hazy sheen (Fig. 3) and sometimes can actually feel “unfinished.”

Cleaners and polishes. No matter what kind of finish is on your instrument, it’s a good idea to keep it clean to prolong its life. There are hundreds of products on the market that claim to be the best for cleaning and polishing an instrument. The truth is many of them will cause the finish to slowly deteriorate. These cleaners contain petroleum products and solvents that can damage a nitrocellulose finish, and some polishes contain abrasives that will remove a vintage instrument’s natural patina. The best guitar care products won’t leave behind residue and do not contain solvents or petroleum products.

There’s a debate about whether polishing a guitar is more harmful than helpful. When you polish a guitar, it creates a seal or coating that’s intended to protect the finish. However, I’ve found that the outcome is more cosmetic than functional, and many finishes don’t benefit from waxing or polishing. Polishes and waxes build up over time and can eventually dampen the sound of your guitar—almost like wrapping it in a bed sheet.

But that’s not all: If your guitar has finish checking, polish will build up in the hairline cracks, and this can discolor the wood underneath or even cause the finish to flake off. Based on experience, I believe cleaning your guitar is more beneficial than polishing or waxing it. Polishing will make your guitar look better, but really doesn’t benefit the finish other than making it shiny. If you feel compelled to polish your instrument, look for products that contain pure carnauba wax—it’s the safest for your guitar.