The “White Heron” castle of Himeji
Before we even begin discussing why instruments crack the number one question on your mind right now probably is “Can I absolutely prevent my instrument from cracking?” The answer unfortunately is ‘no’, BUT there are things that can be done which greatly reduce the likelihood that an instrument will crack. I will caution you right now that there are many opinions about how to prevent cracking and how to properly care for a wooden instrument, not all of which are grounded in an understanding of how wood works.
African Blackwood (grenadilla) tree trunk cross section
The wood which most oboes is made from comes from the African Blackwood tree. It’s also called grenadilla wood, and is similar to other deciduous hardwoods. The section of the tree used for instruments is the center of the trunk, the heartwood. The tree when lumbered is usually cut up into billets of various sizes, taken from the best of the heartwood. Since these trees don’t grow very straight the number of useable billets from each tree is fairly low, one of the reasons the wood is so expensive. It’s just like making reeds where 99% of the harvested cane is eventually thrown away in order to get to decent tubes.
Blackwood billets after lumbering
To understand why instruments crack we need to first take a look at how wood behaves under different circumstances. Let’s look at a blackwood billet, see illustration below:
Note that the grain direction always runs in the same direction as the tree trunk. This is also the major strength axis of the wood. For example, if you were to attempt to split the piece illustrated above in two by striking it with an axe on the end or on the side in the same direction as the grain it would split apart with little effort. But striking the wood across the grain on the side yields nothing but frustration as it will not yield in that direction. Wood is porous and will easily absorb moisture on the ends due to capillary action. It will also absorb moisture through the sides across the grain but not as readily. It’s critical to note here that wood is NOT dimensionally stable across its width, that is, across the grain. Very little expansion and contraction due to moisture occurs along the wood in the direction of the grain, but across the grain the movement is significant, driven primarily by the moisture content of the wood, and to a lesser degree by its temperature.
When a tree is harvested and lumbered, there is a significant amount of moisture in the wood, usually much higher than the surrounding ambient humidity. Before wood can be made into instruments, it must be properly “seasoned”, that is, allowed to reach a stable moisture content. For furniture making a moisture content by weight of around 7% is considered ideal, so to season wood properly it must be stored for several years in an atmosphere of around 35% to 40% relative humidity. Because of the density of African blackwood typical seasoning times are at least 5 years. Once an instrument is machined from billets of blackwood the machining process itself can relieve stresses built up in the wood created whilst the tree was growing. Sometimes these stresses take time to work themselves out after all the machine work is done, resulting in slight dimensional changes to the instrument. This is one reason why there are no two oboes which are exactly alike even though they were made at the same time from the same batch of wood, even from the same tree.
So back to your original question, how do we keep our oboes from cracking? We must do things that minimize wood movement. Since it’s impractical to prevent all wood movement we need to learn to deal with it so that it does not cause cracking. M. Alain de Gourdon of F. Lorée says that cracking typically occurs in cold and dry places around the world. In North America, instruments are particularly at risk because we tend to overdo forced air heating and air conditioning, both of which greatly reduce humidity and can create dangerous extremes of humidity and temperature from one location to the next.
F. Lorée ships a set of instructions with every new instrument on how to properly “break it in”. Following those instructions carefully will greatly reduce the likelihood of cracking:
“The following will help you to get the most enjoyment from your new instrument and reduce the possibility of cracking. The risk can be minimized by playing the new instrument gently during the first few months, and by taking precautions during periods of low humidity.
In the beginning, play the instrument for no more than 10-15 minutes at a time. Swab it, return it to its case and keep the lid closed. A few hours later or the next day, you may repeat this procedure. Each week you may add five to ten minutes playing time. After about three months, you should be able to play it as you wish.
On chilly days (or in cold rooms) always warm the instrument before beginning to play on it. This may be done by holding it against your body for a few minutes, or cradling at least the top joint in your hands. If the oboe was left in an unheated area on a cold day, you must not play it until it has had a chance to warm gradually. [emphasis mine]
Avoid laying down the instrument on a cold or very warm surface or next to a heat source so that it is not exposed to rough variation of temperature. If your instrument is kept in a dry climate, or even during prolonged periods of dry weather, the best is to put a humidifier in the case to maintain higher moisture.
During the break in period, we recommend you to oil regularly the bore of your new instrument (about once a week). Be sure first, that the bore is well dried and cleared of moisture. Then put some drops of “F. Lorée” natural bore oil preferably on a feather and apply a light coat of oil gently inside the instrument. After a few months, you can progressively reduce to oil your instrument.”*
* From instruction sheet shipped with every new Lorée instrument, courtesy of Alain de Gourdon, F. Lorée
M. Alain de Gourdon recommends the use of their natural bore oil or natural almond oil. The idea behind oiling the bore is to reduce the wood’s ability to absorb moisture from your breath that condenses in the bore. Repeated oiling gradually infuses oil into the wood, displacing some of moisture that is there and preventing it from picking up additional moisture from your breath. Ideally at some point the oil will have displaced most of the moisture in the wood such that changes in ambient humidity and temperature will have a significantly less effect on wood movement, greatly lowering the risk of cracking. Also, don’t do dumb things like leaving an instrument in the car where it can overheat and crack in the summer or get chilled in winter. Outside in the winter keep your instrument under your coat. Always use an insulated case.
Oiling an oboe:
Refer to the instructions provided by F. Lorée listed above. Be sure the oboe is dry on the inside before oiling. Do not try to oil right after playing. Use a feather long enough to go through the top joint and stick out of the reed well when you feed it base first from the bottom. This might seem rather cumbersome BUT it keeps the feather from poking into the tone holes and leaving excess oil there which it surely would if you pushed it through from the joint. Put just 2 or 3 drops of oil on the end of the feather, then slowly pull it through while twisting it. Repeat this several times to spread the oil around but don’t add any more oil after the first pass. Feathers work best at spreading the oil around as they won’t absorb the oil. Viewing the bore against a light from the top the inside should be slightly shiny from the oil, but not soaking wet. Note that the first time you oil a new oboe the oil will soak in almost immediately. Keep tone holes pointed up throughout this process to keep oil from pooling in them. Oil can make pads stick so keep it out of the tone holes. After oiling, put the oboe away and let it rest for at least 24 hours to allow time for the oil to diffuse. Oil the bottom joint in the same manner. The end of the bell with all of its exposed end grain will absorb a lot of oil so the best way to oil the end of the bell is to put a drop or two of oil on your finger and rub it in, much like finishing fine furniture. A little bit of oil goes a long way. Too little is better than too much, especially after the first time. I also apply a small amount of oil to the wood under the thumb rest and the first octave key since these areas can absorb a significant amount of moisture from your thumbs.
The use of natural almond oil was mentioned. This is also known as sweet almond oil and is usually available at any health food store or natural market. This is a cosmetic grade (as opposed to food grade) oil. Cosmetic grade oil has stabilizers in it which keep it from getting rancid or gummy. Petroleum based oils should be avoided, these can cause the wood to deteriorate. Vegetable oils should be avoided as well as these will eventually get rancid and gummy. When in doubt use F. Lorée natural bore oil. You should continue to use only the kind of oil that was first applied to the instrument for all future oilings.
Years ago oboe players tended to keep their instruments for much longer periods than professional players do now. The legendary English oboist Leon Goosens played on the same USED Lorée oboe for 40 years and it never cracked. But he was a little extreme in the care of his instrument. Once a year he would remove all of the key work and thoroughly oil it inside and out. He would then allow it to rest to let the oil soak in before reassembling and adjusting it. That’s definitely over the top for most of us. Over oiling an instrument is not a good thing. If there’s too much oil in the wood it will tend to ooze out and cause pads to stick. There is no way to remove excess oil from the wood, so don’t overdo it.
If left to acclimate properly an oboe will be perfectly happy in a tropical country, but in colder climates some effort may be needed to maintain a minimum level of moisture content in the wood. There is a lot of FUD surrounding the use of humidifiers in one’s instrument case. Some people even put orange peels and other silly things in their cases in order to raise the humidity inside. Don’t do that. Only use a device specifically designed to perform this task. Remember that humidification is called for only if the instrument will be kept for long periods of time (more than a day or two) in an environment where the relative humidity is low. In North America relative humidity indoors in the winter can drop to 20% or below due to excessive heating. A humidifier is called for if the humidity in the environment where the instrument is stored is below 40%. As with oiling, humidification can be over done. Excessive moisture will cause the wood to swell, leading to all kinds of unwanted movements, possibly even cracking. The sound will be affected as well.
Why oboes crack:
Note that an instrument will take up moisture somewhat more quickly than it will release it, which is why it’s so important to oil it and to control extremes of temperature and humidity that an oboe is exposed to. Cracks occur due to a buildup of stress in the wood because of differences in moisture content and temperature between the bore and the outside surface of the oboe, almost always in the top joint. The top joint is particularly vulnerable to cracking due to its smaller overall diameter than the bottom joint, the greater difference between the inside (bore) diameter and the outside diameter, and higher temperature saturated air from the player’s breath, which is much cooler by the time it reaches the bottom joint.
Relative cross sections of the top joint (left) and lower joint.
Warm moist air passing through the top joint diffuses moisture into the sides of the bore, and along with the warmth causes the wood to swell. Compression stresses build up in the center and work their way outward against tension forces from the outside in until something gives and a crack opens up.
Crack formation in the top joint
This is why cracks usually appear on the outside surface and may not work their way through to the bore. Remember that across the grain of the wood is the weakest strength axis, which is why cracks typically form along the length of the top joint or between the tone holes. Reducing moisture absorption in the bore goes a long way to help prevent cracks, hence the need to oil early and often in the life of a new instrument, and to carefully maintain its environment.
Post copyright (c) 2016 Jeffrey W. Sutherland. All rights reserved.
comment_form