Here in the fluteshop, we like to take every opportunity to remind flute players and our customers that like many musical instruments, wood flutes are quite sensitive to humidity and will swell or shrink as the wood absorbs or loses moisture from (or to) the surrounding environment. In the wrong conditions it's quite possible for a flute to crack, and even though we take great care to season our wood properly to reduce this risk, there are some steps you must take if you share your home with a flute or travel with one. If you can't find a "flute terrarium" like this one, never fear! There are some simple things you can and should do to protect your flute.
The first thing to be aware of is the ever-changing relative humidity (RH) in the geographical area and individual living space in which the flute is kept. While it's not important to understand all of the relevant physics (we can't all be meteorologists, right?), note that the volume of moisture needed to reach a given RH changes with air temperature—thus in winter, conditions tend to be drier, especially indoors with forced-air and most other heating systems. As far as we have been able to ascertain, the ideal humidity range for a wooden flute is about 45-60% (possibly 50-60% for antique flutes which may not tolerate drier conditions as well as modern ones). However, indoor humidity in a home can be much lower: easily 25% in many areas of the U.S. and so extra care is needed to protect your flute from the possibility of cracking.
Step 1: Get an Accurate Hygrometer
In our experience, these things aren't always calibrated correctly, so its a good idea to
get a several and check them against each other. If you have three or four and they all agree except for one, you can be reasonably certain that those with similar readings are correct. If you get the type with an additional sensor and place it outside, you'll be able to see what the outdoor conditions are as well. This can give you a heads-up when there is a change in the weather and it's about to get dry indoors.
Step 2: Keep an Eye on the Humidity
Depending on where you live, the climate may be more or less of an issue. Ireland for instance has wetter weather than most places in the U.S., but even in wet climates, indoor
humidity can be much lower than outdoor, depending on how the home is heated or cooled. It's a good idea to swab excess moisture out of the flute after playing and to keep a hygrometer in the case as well. This is especially important when traveling. Alternatively, in
very dry conditions it may be beneficial to refrain from wiping all of the moisture out of the flute and allow the condensation inside the bore to keep the conditions in the case from drying out. A smaller device like the one seen at right can be placed inside the case—particularly critical when going from a relatively wet climate to a drier one. For example, if you live in Virginia and take a trip to Arizona, be aware that you're moving from a medium-humidity environment to the literal desert and need to take extra precautions. No one wants their flute to end up like this...
Step 3: Ideas for DIY Humidors
Depending on the above variables, it can be quite difficult to maintain the proper humidity. During a recent test we performed at home, the RH was below 30%, even after running a humidifier on high for 48 hours. In this instance it is best to keep flutes in something with a sealed vapor barrier, even if it is just a large, heavy-duty ziplock bag. We have yet to find an affordable humidor option designed for flutes, so start with a bag with a hygrometer inside and then work your way up from there.
The next step up and the simplest is a plastic tub with a rubber seal integrated into the lid. One of these made by Sterilite is a good solution, especially if you have multiple
flutes, and the clear sides allow the hygrometer to be seen without opening the lid. The rubber seal is important because the bins without them tend to dry out too quickly. You can place a cut half of an apple or a damp sponge inside to act as a time-release moisture holder and then keep an eye on the hygrometer so you know when to change it out.
If you really want to go all the way down the RH rabbit hole and make something a little nicer to look at, it's actually not difficult to make a home humidor out of a wall cabinet with a few basic tools. Our in-house mad genius Aaron Olwell created one for flute parts in the shop by sealing around the door of a wall cabinet with foam rubber, cutting a hole in the door (that is then taped over with clear tape), affixing a hygrometer to the inside, and then putting in a moisture source. Some trial and error may be needed to get the right amount of moisture going inside, but then you have a stable place where it is easier to control the RH.
However you choose to do it, don't forget to monitor the environment in which your flutes are kept, and make sure it doesn't get too dry. Remember, a dry flute is a sad flute!