Through the years, I have fielded many o’ question about guitars and other fretted instruments. I have always maintained the philosophy that “If I don’t know the answer, I will find out”… Now… I may Bull$#!+ about Football, TV Programs and  Women (Seriously, who actually KNOWS about women?) but I will NOT just “make up” an answer about the maintenance of guitars… I gotta’ have my priorities, right?
 
    By far, the most questions were with relation to humidity and how changes affect fretted instruments.
 
    In Arkansas, we are cursed AND blessed with humidity. In the summertime, when the livin’ is easy, we may have a humidity of 80%… and in winter, the temperature drops, and if you have live in an older house or do not have a humidifier installed in your HVAC system, our furnaces kick on and relative humidity can drop as low as 20%.
 
    This swing in relative humidity can wreak havoc with our fretted friends.
 
    First, lets make clear what REALATIVE HUMIDITY actually means.
 
Technically Speaking
     I’ll try to explain Relative Humidity (RH) as simply as I can. The word “relative” is used because it changes as temperature changes. If, for example, on a cold winter day it’s 30 degrees (Fahrenheit) outside with an RH of 50%, and that air enters your home and is heated to 70 degrees, the humidity drops relative to the temperature. In short, the amount of moisture in the room is the same, but since the warmer air is capable of transporting more water vapor, the “relative” humidity drops.
Now, to confuse that matter even more, there is a common misconception concerning water vapor and air.
    Please notice that I stated that air TRANSPORTS more water vapor… I purposely did not say “HOLD” more water vapor. Here’s why:
    Often the notion of air holding water vapor is presented to describe the concept of relative humidity. However, air simply acts as a transporter of water vapor and is not a holder of it. Water vapor does NOT BOND to air or the gasses that make up breathable air… For this reason, relative humidity is generally understood in terms of the physical properties of water alone and therefore is unrelated to the concept of absorption of water vapor in air. In fact, water vapor can be present in an airless volume and therefore the relative humidity of this volume can be readily calculated.
The misconception that air holds water is likely the result of the use of the word saturation, which is often misused in descriptions of relative humidity. In the present context the word “Saturation” refers to the state of water vapor, not the solubility of one material in another.
    The thermo-physical properties of water-air mixtures encountered at atmospheric conditions are reasonably approximated by assuming they behave as a mixture of ideal gases. For many practical purposes the assumption that both components (air and water) behave independently of each other is reasonable. Therefore the physical properties of an air-water mixture can be estimated by considering the physical properties of each component separately.

Got it?

    Well, if you’re scientifically oriented, then this probably makes sense. If you’re not, just understand this:
When you heat air, the humidity drops. And by drops, I mean it plummets. It’s easy to lower the RH in your house to 10% just by heating it.
     Now that you are all Ed-U-cated… Let’s get to those question:
     How does relative humidity affect guitars?
Wood will try to equalize to it's surrounding air, in temperature and humidity. If wood becomes too moist it will swell; on the other hand, if wood gives up it's moisture, it will shrink. All are physical characteristics of wood.
     What is the desired level of humidity?
45%-55% relative humidity is optimum. If this is obtained, you minimize the risk of damage. This is the relative humidity the Martin Guitar factory maintains.
     What if my guitar has been subject to excessive humidity?
If your guitar has been exposed to excessive humidity seams may separate, bridges may become loose and your action may become unplayable. A dehumidifier is recommended if your guitar has seen these changes.   
    What if my guitar has been stored in a dry environment?
Low humidity seems to be more of an issue. As your guitar dries, the wood actually shrinks. This results in the top lowering and the strings come with it. All of this stress results in the wood cracking. To solve this problem you should invest in a humidifier. Be sure to also get a hygrometer to measure how much humidity you bring into the air.
     What happens to my guitar at 60% humidity?
At 60% relative humidity or above symptoms may include tarnished frets and strings, corrosion to nickel, chrome or gold plating on tuning machines, swelling of the top, high action and loose braces and bridges.
    What happens to my guitar at 50% humidity?
At 50% relative humidity your guitar is in good condition.
    What happens to my guitar at 40% humidity?
At 40% relative humidity you may see sharp fret ends. This is the area of the fingerboard that extends over the body that may begin to crack slightly from the 12th or 14th fret toward the soundhole.
     What happens to my guitar at 35% humidity?
At 35% relative humidity your top will begin to shrink. The soundboard may look and feel rippled or dried in. The sharp fret ends seen in 40% relative humidity will become more evident.
     What happens to my guitar at 30% humidity?
At 30% relative humidity you may see cracks in your guitar. Even if you do not see a crack in the guitar, it has still lost moisture and the top has begun to sink. To make your guitar playable you may need a higher saddle.
    What happens to my guitar at 25% humidity?
At 25% relative humidity more cracks are seen. Fret filing may be needed.
     How can I maintain that magic number of 45-50% humidity?
First… Have your guitar checked out by your trusted guitar technician or Luthier for any damage or dangers. If they are “worth their salt”, they can usually look at your instrument, maybe take a few measurements, feel around and mumble “Hmmmm” a lot… and determine the condition of your instrument. THIS SHOULD NOT COST YOU A PENNY!
     If the tech finds an anomaly, they will offer a suitable solution… THAT might cost just a little but when it comes to your “baby”… are you really gonna’ “cheap out”?
 Solutions-
Here are some simple steps you can take to protect your guitar from the ravages of low humidity, and to keep your guitar in optimal condition for a lifetime of great playing.
    1. Store your guitar in its case… Make that a HARD case. Not a gig bag or one of those nifty hard foam, canvas covered, lightweight thingys… A wood, plastic or composite formed case will shelter your guitar through many extreme conditions. I realize that guitars are beautiful. You want them readily at hand but a stand or wall hanger is not the best place for them to live unless you are humidifying the whole house… or you have your own private “Man Cave”… or, to be PC about it…“Woman Cave”. In Arkansas we are luckier than most. We can get away with hanging our instruments in the open during the humid summer months… but make no mistake… when fall comes and the furnace kicks on, put your beloved axe in the case along with one of the popular humidification devices.   
    2. Use a simple humidifier in your guitar case during cold winter months or at all times if you live in a dry climate. You don’t have to overdo it. It is possible to cram too much water down the throat of your guitar, so easy does it. If your humidifier goes bone dry, give it a drink and put it back in. In the end, you might not need to re-wet it more than once or twice a month.
    3. Keep a digital hygrometer enclosed in your case and look for 45–50% readings. I have them in my shop for $20. Only use digital; the analog ones that come with a barometer are not accurate.
    4. Learn to “read” your guitar by noticing sharp frets on any guitar—electric or acoustic. On an acoustic guitar, low action can indicate either a dry or a wet guitar – Depending upon, which is distance of the strings from the frets. When the humidity gets very low, small ridges and valleys appear on the solid wood surfaces. This is sometimes called scalloping. These are signs of drying wood. When you see this, put the guitar in its case and give it a dose of humidity. Usually, the sharp frets and scalloping will go away.
    5. If you choose not to store your guitar in its case, at least put it there for one week per month with a humidifier. Think of it as a week at the spa. Your guitar will thank you.

My Take on it-
    Ya’ know, I love to see wear and tear on guitars from PLAYING. Believe me I do. My favorite thing to see is a guitar that’s been played to death—sporting holes, scratched-off finish and other evidence of miles and miles of good use. But the damage done by dryness breaks this poor guitar tech’s heart. So, know that with just a little care on the player’s part can mean the difference between an instrument’s long musical life or a short one.
    If you have Frets about Frets or a general fretted instrument question to which you need the answer, please email your inquiry to bryon@littlerockfrets.com. I’ll answer it and maybe include your inquiry in next month’s “Frets About Frets” column, I look forward to hearing from you.
    Bryon Knight owns Little Rock Frets, Fretted Instrument repair, sales and service – (501)681-5712.