Here are some basic cleaning procedures to keep your guitar looking it’s best.
General Cleaning
Most surface dirt and dust can be removed with a soft, clean rag. Cotton T-shirts or 100% cotton flannel work the best. Some companies sell buffing cloths made of flannel, often packaged together with a bottle of guitar polish. If your guitar has spots that won’t come off with a dry rag, moisten your cloth slightly (don’t get it sopping wet!) with warm water and clean a section at a time, turning the cloth frequently to avoid putting the dirt back on the guitar.
After this procedure is done, you can buff the instrument with guitar polish and a clean rag to remove any other surface dirt and shine the finish. If you have a hazy or sticky spot where your skin frequently touches the guitar’s finish, try cleaning with a dry rag first, then with polish. It may take several buffing sessions over some time to get rid of a cloudy finish.
Dirty Finishes
If your instrument is extremely dirty, clean it first, and then use polish. If you polish a real dirty guitar, you will end up just pushing the dirt around or putting the polish on top of the dirt. First, wipe or vacuum off any loose particles of dirt. Then clean with a soft rag moistened in warm water as described above. You can remove stubborn dirt with Naphtha (a solvent), but make sure you use gloves and work in a well-ventilated area to avoid breathing too much of the fumes. Next, use a good quality guitar polish, and then buff with a clean, soft rag to bring out the shine.
Vintage Guitars
Older guitars often have a thin finish that enhances the tone. Always clean these with a soft, dry rag first – polishes are designed to penetrate a finish and add softness and flexibility – this may not be beneficial to an old guitar, especially acoustic instruments. Be careful with vintage finishes that are thin or “checked” (small cracks in the instrument’s finish).
If you polish these with commercial guitar polish, you may end up forcing polish through the cracks and into the wood! Warm water (slightly damp rag) can be used, but again, be careful of working water down into the cracks. A good cleaning method to try for these cracked or thin finishes is to get your face close to the instrument and breathe warm, moist air onto it and immediately wipe off the dirt with your cloth.
Some older instruments (especially those made before the 1930′s) may have a finish made of lacquer or varnish that has become soft or sticky. Don’t try to rub or polish these finishes as you might make the condition worse! Consult your local repairperson as to whether the finish can be restored.
Fretboards
Products are sold to protect fingerboards, but generally, these are not needed. The natural oil in your fingers will be absorbed somewhat by the fingerboard and usually will be enough to keep the wood conditioned (unless, like me, you have dry hands). Occasionally a fretboard may develop tiny hairline cracks due to an arid climate. To avoid this condition, rub a few drops of mineral oil (linseed or lemon oil works well) into the fingerboard once a year to restore moisture and keep the wood from drying out. Make sure that you wipe off any excess oil with a dry rag.
If your fretboard has built-up dirt and grime on it, you can remove this with some extra-fine #0000 steel wool. Pinch a piece between your thumb and forefinger and use your thumbnail to get into the corner between the fret and the wood. If the dirt is especially thick, try using the edge of a credit card or any other thin, stiff piece of plastic to scrape the dirt off of the wood. Follow up with the mineral oil application.
As a final note–don’t use furniture polish on your guitar–most of these have oils in them that stay on top of the guitar’s finish. Most modern polyurethane, polyester, or even new lacquer finishes that are free of checking can be cleaned and polished quite frequently. Consult the manufacturer of your new guitar about the type of finish and recommended cleaning procedure.