If you’ve had a bit of experience playing or fixing unrestored vintage guitars, then chances are you are aware of the sight of very small cracks appearing all throughout the finish. It is described as finish checking and it is particularly typical on aged guitars that have a lacquer finish, but could possibly appear on new instruments also under the right (or wrong) circumstances.
Lacquer is a very “breathable” finish. It has the ability to contract and expand with the wood of the guitar while it moves through a range of temperature and humidity levels. This is an important feature on high quality instruments given that it isn’t going to lock the wood of the guitar below the finish as would a polyurethane finish, which won’t expand and contract similarly.
Nevertheless, the disadvantage is that after some time the lacquer finish can begin to crack or “check” as it is typically described as. If you’re in the camp that doesn’t want to see this on your guitar, you will be wise to pay attention to this warning when dealing with a lacquer finished instrument which has no current checking.
Should your guitar be subjected to cold temperatures, say in the rear of an automobile, for an extended duration (even in the hardshell case), never pull the guitar out and expose it to room temperatures as soon as you get it inside. The guitar will need to have time for it to slowly adapt to the new warm temperatures, so leave it in the case until it has had enough time to do so. Otherwise your lovely laquer finish will likely commence to crack as the wood in the guitar heats up and begins to swell before the lacquer has a chance to adjust.
Poorly humidified guitars can also be a factor in finish checking, normally as a result of drying out. So keep the humidity correct at between 45-50% and ease into temperature changes and you should be good.
While I undoubtedly would not be happy to see this occur to a brand new $4,000 guitar that I just acquired, on a vintage guitar I look at things just a bit different. I could never think about a finish-checked guitar from the 1950’s or 1960’s as less than desirable. Nor would I ever think of refinishing one.
As I said there are two schools of thought on this subject however the natural finish checking, if you ask me, creates a degree of individuality and history that you simply can’t obtain on a fresh, new guitar. Each knick, ding, buckle scrape and finish fracture is a part of the battered history of the instrument. Every musician who picked it up and played it left a tiny bit of himself behind. All those campfire melodies, lounge room singalongs, bar room gigs and late-night jam sessions are all right there, and the finish cracks are a part of that story.
I would personally not ever wish to obscure that beneath a glistening finish. We have new guitars for that.