PRESCRIPTION FOR WOOD ROT: A DECAYING PROBLEM
Dr. Yoshiyuki Ishikawa,
University of Nevada, Las Vegas
Problem
A common problem associated with bassoons, especially poorly maintained and old bassoons, is wood decay: a process of decomposition caused by fungi or bacteria as a result of constant exposure to moisture. According to the "Wood Handbook" published by the U.S. Department of Agriculture,
"Serious decay occurs only when the moisture content of the wood is above the fiber saturation point (average 30 pct.). Only when previously dried wood is contacted by water, will the saturation point be reached. The water vapor in humid air alone will not wet wood sufficiently to support significant decay, but it will permit development of some mold. Fully air-dry wood usually will have a moisture content not exceeding 20 percent, and should provide a reasonable margin of safety against fungus damage. Thus wood will not decay if it is kept air-dry, and decay already present from infection incurred earlier will not progress". [1]
The above quote refers to dried untreated wood. Bassoons are manufactured from dried and cured wood, and if properly maintained, wood deterioration will not occur. However, when any part of the wood on the bassoon is constantly exposed to water, wood decay can occur. Wood decay frequently occurs in the following areas.
1. The unlined section of the bore adjacent to the u-tube in the boot joint.
2. The unlined tone holes C, B, G-sharp and A in the boot joint.
3. The G-sharp and A pad seats in the boot joint.
4. The unlined tone holes F, E, and D in the wing joint.
If neglected and untreated, wood rot can spread, requiring costly major repairs. However, if detected and if the damage is minor, it can be restored by the following procedures outlined below. Moreover, with proper maintenance, wood rot can be prevented.
Diagnosis
Wood rot can easily be diagnosed through visual and tactile examinations. The damaged part is usually characterized by an uneven discoloration of the wood which usually appears dark brown or gray. The texture of the wood will show signs of decomposition such as fragile soft moist surface, and an uneven corrugated wood grain. Wood rot may also appear as a dry, brown, crumbly rot, sometimes called "dry rot". Wood often can be scraped off with a fingernail, or in the case of the tone holes, by rubbing their interior with a moistened swab. If after cleaning out the initial accumulated dirt the swab surface continually remains brown, indications are the wood is deteriorating.
REMEDIES AND CURES
There are several procedures to repair the damaged areas. Each procedure is determined by the degree of damage.
Minor Damage
Surface damage characterized by rough texture and discoloration.
REMEDY: oil treatment
For oiling the bore use only RAW linseed oil. Raw Linseed oil can be obtained from any paint store. If Raw linseed oil is not available, use PURE olive oil. Absolutely do not use boiled linseed oil, since it will not absorb into the wood.
1. Remove all pads from the affected area.
2. Clean off the dust and accumulated dirt and oil with a cotton swab or a cloth.
3. Apply oil heavily with a cloth or a swab.
4. Wipe off any excess oil to prevent oil run-off. Avoid oil from running into the lined bore. If oil runs into the lined bore, wipe it off COMPLETELY before it dries. Oil can react with the ebonite lining, and may cause damage.
5. Let the oil absorb into the wood for 5 to 6 hours. During this process, rotate the bassoon several times to evenly distribute the oil. For the first hour, rotate the bassoon at least twice; thereafter, rotate every one to two hours. Rotation is especially important when oiling the bore or the interior of the tone holes, since it equally distributes the oil.
6. Repeat the above procedure two to three times, or until the wood no longer absorbs the oil. After the final coat, wipe off ALL excess oil completely before it dries. This is especially important to prevent oil coagulation on the wood surface.
7. Let the oil dry THOROUGHLY for several days. The drying time is contingent upon humidity and temperature, and should last anywhere from 2 to 7 days. Test for dryness by applying tissues to the oiled area. Oil should not be present on the tissue. It is imperative that the oil be dry before placing the pads back on the bassoon to prevent hardening of the pad leather.
The procedure should correct any existing minor problems, and should further prevent
the damage from spreading. Check the effected area in about 6 months. Repeat the above procedure if necessary.
Minor damage can also be repaired by an alternative method, using shellac dissolved in alcohol. Will Jansen writes in The Bassoon,
"With all types of bassoons, there is a weak spot, this is the lowermost section of the wide (ascending) bore of the butt joint, which, in the Heckel type, is not lined. Here the wood is exposed to the moisture ascending in the slight air stream and, in case much moisture collects in the metal u-tube, here in the course of years the wood may rot and it is a good practice for; every bassoonist to inspect this part frequently, and still better, to treat the lower section of the u-tube with a thin layer of shellac solved in spirit. This very volatile substance is put on with a soft painter's brush quickly.
"The same moisture attack on wood may take place in some of the open finger holes and key holes, particularly those descending on the outside. Here the same remedy is recommended; a thin covering of shellac in spirit, in this case very thin, so as not to alter the diameter of the finger holes." [2]
The method suggested by Jansen may be effective in repairing minor damages quickly, especially the exterior pad seats of the tone holes. However, it is this writer's opinion that shellac does not penetrate the wood as well as oil. Therefore, when this method is used to repair tone holes and the bore, shellac may collect and harden on the wood surface, altering the bore or tone hole dimensions.
Moderate Damage
In addition to the characteristics listed under minor damage, the affected areas may appear gouged, chipped, or worn, indicating moderate damage. Depending on the location of the damage, it may be necessary to restore the gouged, chipped or worn-out wood with wood filler. Wood filler is especially necessary, if the damaged area is a pad seat. Worn-out or damaged pad seats will prevent proper pad adjustment, and will cause air leakage. When the interior wall of the tone hole is chipped, it is necessary to fill it with wood filler only if the pitch from the specific tone hole is uncontrollably or abnormally sharp. (Any alteration involving the bore should be avoided due to its sensitive acoustical nature.) It is highly recommended to use non- epoxy based wood filler such as MATCH WOOD. This product is easy to work with, and if necessary, can easily be removed without damaging the original surface.
Before following the procedure below, oil the effected area by following the instructions under minor damage.
PROCEDURE FOR FILLING THE DAMAGED AREA WITH MATCH WOOD
1. Be certain that the surface to be filled is clean and completely dry.
2. With a small spatula or a screw driver, fill in the damaged area to a height just above the original surface (.10 mm aprox.). Let it dry. See Diagram 1.
3. Lightly sand the dry wood filler with #400 sand paper until flush with the original undamaged wood surface. Take caution to avoid sanding the unaffected areas.
4. If necessary repeat process 2 and 3.
5. If adding filler to a pad seat, be certain that the edge of the pad seat closest to the tone hole is the highest point. Be certain that the tone hole rim is the same height around the circumference. Check and adjust pads to their proper seating by using paper shims. See Diagram 2.
Extensive Damage
Extensive damage requiring total reconstruction of the tone holes and pad seats can be made by following the procedures listed above. Fill the damaged area with wood filler and sand it down to the proper dimensions. However, such repairs require accurate measuring devices such as micrometers, telescopic gauges, or a dial caliper. Also, it is imperative to have accurate original tone hole dimensions, which can only be obtained from the manufacturer, or by measuring bassoons of the same make, and with similar serial numbers. Unless tools and accurate measurements can be obtained, reconstruction procedures should be avoided.
Prevention
Wood rot can devastate an instrument. Just as easily, it can be prevented by following simple maintenance procedures:
1. Avoid exposing the unprotected wood to moisture.
2. Never lay the bassoon down when the bore is wet.
3. Swab the instrument after each use in the order of: 1) small boot joint, 2) wing joint. Always pour the accumulated water in the u-tube from the lined small bore of the boot joint.
4. If the tone holes are not lined, swab them out with a cotton swab after each use.
5. Lightly oil the bore and tone holes once a year.
Bibliography
1. Wood Handbook: Wood as an Engineering Material. U.S. Department of Agriculture. Agriculture Handbook No. 72. Revised August 1974. 17-3. [return]
2. Jansen, Will. The Bassoon. Part V. p. 688. Fritz Knuf Publishers, Buren, The Netherlands. [return]
DR. YOSHIYUKI ISHIKAWA holds degrees from Northwestern University (B.M.E. and M.M.) and the University of Michigan (D.M.A.). He has studied with Lewis Hugh Cooper, Bernard Garfield, Norman Herzberg, and Wilbur Simpson. He is currently Assistant Professor of Music at the University of Nevada, Las Vegas, principal bassoonist in the Las Vegas Symphony and Chamber Players, and in the Nevada Wind Quintet.