Checking and a Vintage Acoustic - Cleaning and What to Check

Cleaning the Body

The fine layer of nitrocellulose lacquer contributes to the unique resonance; however, this finish is porous. The silicones and waxes in many household products accumulate in fine cracks in the lacquer and with continued use eventually deaden the sound. To remove grime and extend the life of the lacquer, always use a cleaner designed for vintage instruments, such as a restoration kit or other vintage finish cleaners.

The finish may 'fog' if there is water in the cleaner and this will dissipate as it 'dries'. Fogging and white haze can also be cleared using isopropyl alcohol (IPA). Dab some on a paper towel and fold it over then place the dry side on the finish and cover it with your hand.  After a few minutes the IPA vapor will soften the finish allowing the trapped water to dissipate.

Apply a dab of cleaner to a soft cloth, rather than to the instrument itself. Rub it gently over the woodwork to remove dust and dirt. Use a clean microfiber cloth for each new area of the body until the whole instrument is clean. Finally, use another cloth to buff away any excess residue.

While it is tempting to polish a vintage acoustic guitar to a high shine, this risks buffing away the delicate nitrocellulose finish. Also, polish tracks through cracks in the lacquer, which cause it to flake and lift away and the wood beneath it to discolor. In addition wax in some polishes will fill cracks with white residue impossible to remove so be careful to select the correct product for vintage guitars. Most owners of vintage guitars prefer to accept a softer, satin finish that shows the instrument has age and character, rather than pursuing a perfect high shine.

Signs of an old refinish? 

John Arnold shared this list on UMGF many years ago. 

• The easiest way to tell is to look for finish where it isn't supposed to be, namely, on the edge of the fingerboard over the body. Martin only started putting finish there in the last few years.

• On Martins, the neck and body are finished separately, so there should be no finish filling the joint.

• Although Martin will always remove the bridge to do a refinish, it is rare that they also remove the neck. Look for finish in the neck/body joint, or evidence of sanding. If the neck is removed, a step in the body wood (indicating sanding after the neck was installed) or discontinuous finish are clues of a refinish.

• Any finish filling in dents or dings could be from refinish, overspray, or lacquer touch up. In that case, the newer finish can be distinguished because it will fluoresce a different color than the old finish under ultraviolet light.

• Also, if the peghead face was refinished, the decal may be from a later period than the guitar.

• Finally, if you see a lot of crazing on the celluloid binding and/or pickguard, then a refinish is likely. Additional lacquer solvents applied to the celluloid can cause it to shrink excessively, creating the cracks.