Check it before you wreck it: Extensive finish checking on the upper bout of a Telecaster® Thinline guitar.
Guitars with nitrocellulose lacquer (nitro, for short) finishes, especially older ones, are often subject to a condition called “finish checking.”
A checked finish has nothing to do with little squares; it has everything to do with the appearance of fine hairline cracks in the finish that run in all directions, imparting a mosaic-like appearance. Whether it’s a little or a lot, finish checking is extremely common. A lot of guitarist, bassists and vintage enthusiasts who dig the beat-up look actually like finish checking because its presence conveys a sort of battle-hardened authenticity presumably conferred by years of wear and tear.
Like it or not, finish checking is a climatological phenomenon created by rapid changes in temperature. It happens most often in winter, when a chilled instrument is exposed suddenly to warm air—for example, when a guitar case is immediately opened in a warm venue or studio after sitting in the car for a while in cold weather.
What happens in the event of such a sudden temperature change is that the wood expands. Wooden musical instruments are always expanding and contracting based on their environment and moisture level at the moment, and some instrument finishes are better at going with the flow, so to speak.
Nitro, for all its other wonderful qualities, isn’t one of them. When a nitro-finish guitar is brought in from the cold and exposed to sudden warmth, the wood expands faster than the lacquer, which cracks under the stress. To make a somewhat extreme comparison, it’s kind of like when Bruce Banner turns into the Incredible Hulk—he gets all big and brutish and rips right through his own clothes, which of course do not grow with him (good thing those pants are stretchy).
Finish checking eventually does happen to a great many nitro-finish guitars and basses, at least lightly. The good news is that it doesn’t affect the sound of an instrument. The might-be-but-might-not-be bad news is that once finish checking has occurred, there’s no real way to repair it except for completely re-finishing the instrument (and you probably don’t really want to do that, especially on an older Fender instrument). As noted though, if you’re one of the many players who actually take pride in its badge-of-honor presence, you might not consider finish checking a problem in the first place.
To prevent it, though, an important precaution can be taken. The best thing you can do for an instrument chilled by travel or shipping is to let it gradually acclimate to room temperature before opening its case. Give your guitar the time it needs to warm up before unpacking it, and you’ll both continue to rock on with unchecked abandon.