If you have lived in any northern climate with seasonal changes in weather, temperature and humidity, this article is for you. As a double-bassist for the past 30 years and a luthier for the past 21 years, I have traveled with my instruments in many different climates, with varying humidity levels and temperatures and have seen the effects of this on both older and newer instruments. During the past two winters (2013-14, 2014-15) the North American continent has experienced extremes in heat and cold, accompanied with extremes in humidity levels. These changes in humidity are only exacerbated indoors through the various methods of heating a house, apartment, or university practice room. As a luthier, I have seen the results of these extreme fluctuations. If you are the owner of a violin, viola, cello or double-bass, it is very important that your knowledge about the effects of humidity on wood be more than internet forum hearsay, or other such misinformation. The health of your instrument depends on you!
Instruments of the violin family—violin, viola, ‘cello, and double-bass—are traditionally made of air-dried wood and glued together using animal hide glue. Through a bonding process of cohesion and adhesion, hide glue creates a very strong, yet flexible and reversible glue joint. For this reason, wooden musical instruments are able to expand and contract with the humidity changes, ideally without a seam opening. The tension due to this expansion and contraction at times may result in the opening of a seam. Ultimately, an open seam is the best possible outcome for your instrument, rather than a crack opening on the top or back. Hide glue is unique in that is water soluble and an old glue-joint can be re-opened, cleaned out, and re-glued over and over again, creating a bond as strong as the original. This is due to the hydrogen bonding property of water-based glues. Hide glue has great capillarity and wetting properties, with the hot glue mixture being carried into the pores of the wood. In contrast, PVA glue (polyvinyl acetate)—commonly known as “wood working glue” or “white glue”—behaves differently. PVA glues are water-based emulsions which when cured, form a water-resistant bond through the process of evaporation and polymerization. There are many of these popular wood-working glues on the market and they do serve a specific purpose in woodworking. While it saves time in assembling a commercially made wooden musical instrument, it can cause future repair-related problems. White glue is a “surface adhesive” glue and after the clamping action has pushed white glue into the wood pores, a very thin layer of glue remains between the two wood surfaces. The glue in the pores of the wood then hardens and is nearly impossible to completely clean. Once dried, white glues are no longer water-soluble. The use of PVA glue becomes an issue when an instrument initially glued with white glue is then repaired using hide glue. The “new” glue joint will always be a point of weakness, due to the clogged wood pores. While the various PVA glues and epoxy resins have certain advantages over hide glue in very specific instances of bow and instrument repair and restoration, only hide glue should be used in the making of a new instrument and the repair of an older instrument.
The wood used in making of the instruments is ideally cut at the proper time of year, air-dried to the proper humidity level, and stored in the proper manner. Unfortunately, the world is not ideal. It is simply not possible to have knowledge of this unless you personally know the maker of your instrument and have knowledge of his or her wood dealers and their harvesting and drying processes.
Wood is hygroscopic. This means that any given piece of wood adjusts to the environment’s humidity level by taking in moisture or releasing moisture. Freshly cut logs have “free” and “bound” water. “Free water” is water in liquid form that travels through the cell lumens of the wood. “Bound water” is water which is attached by hydrogen bonds to the woods cell walls. Although this is an oversimplification, during the drying process the free water is what leaves the wood and the bound water is that which remains. When completely dried and stable to that point the wood is stable enough to use, the woods cell walls are fully saturated and expanded because water has bonded at all possible connections. This is “fiber saturation point” or FSP. In a nut shell, this is why wood shrinks and swells according the humidity in which it is kept.
If this humidity change is too sudden, the wood will not have time to adjust without either a seam opening on your instrument or worse, a crack opening on your instrument. As the temperature in a house or apartment rises, the humidity moves lower, regardless of heat source. While cold can affect the playing of a musical instrument, within a certain range of temperatures it is generally not harmful, just uncomfortable. Lack of humidity is more of a concern. Even if you run a fireplace for winter heat, the humidity will still drop as the temperature rises. Some things to look for on your instrument that might be signs of wood movement:
-buzzing or rattling sounds due to open seams
-nasal or muted sound
-a wolf-tone where previously there was none, or a more obvious wolf-tone (this could even be as subtle as a bow skating across the strings, when it normally would not.
If you note any of these things, it is imperative that you seek the services of a trusted, professional luthier as soon as possible to repair your instrument, to prevent any further damage to your musical instrument!
Your Musical Instrument
Seasonal changes in humidity present unique problems to wooden musical instruments. Seams opening up are not uncommon and part of the routine maintenance involved in ownership of a string instrument. When the weather changes and you find the need to run the heat in your house or apartment, it is also time to run your humidifier. What?? You DON’T have a humidifier??!? The sponged filled hoses commercially available by the name “Dampit” are good start towards proper humidification but are they are not enough for most instruments. This will only humidify your instrument while in the case or gig bag, but is not sufficient. It is your responsibility to make sure your instrument is kept in a properly humidified environment. The amount of money spent on an instrument or the variety of wood used in the construction of your instrument does not absolve the owner from responsibility and proper care and maintenance. As a luthier, I guarantee all of my work under normal use and circumstances, and my clientele can rest assured that I will take appropriate measures during the repair and restoration process to make sure that things will not “blow apart” or new cracks develop after the work is finished. However, I cannot and do not extend any warranty in cases of obvious neglect, poor care and maintenance, and mishandling of an instrument. It is extremely rare that a crack is the result of a previous repair or restoration, and the removal and subsequent re-gluing of an instrument’s top is not why a crack opens up on an instrument.
Every string player who owns a wooden string instrument should purchase two very important items: a hygrometer and a humidifier. Both can be purchased at most local hardware stores and home stores. The hygrometer will allow you to be aware of regular room temperature and air humidity, thus letting you know when you should turn on your humidifier. As of February, 2015, a good digital hygrometer can be bought for $12 to $25. A decent sized humidifier can be bought for $120 – $200, a minor investment in comparison to the cost of your musical instrument. In my Chicago workshop at any given day, I have 35-40 double-basses strung up and at tension, thus a large investment. While most of these instruments are older double-basses, there are usually 8 – 10 that are newer instruments. For humidification of my workshop environment (approximately 1,200 square feet, with forced-air heat), I use a “whole house” humidifier with a total 5 gallon capacity, and a wicking type of filter. I have two of them: one for the front “showroom area” and one for the back work area of the shop. I strive to keep the humidity level at about 40%. At times it might go as low as 35%. A humidity level below 30% is cause for concern; below 25% is cause for alarm. Humidity control involves constant monitoring day and night, but this is the price to be paid for living in Chicago and enjoying our lovely winter season.
Cracks and open seams are a constant concern with a wooden musical instrument, but if proper measures are taken to keep consistent humidity levels, they can be a rare occurrence. This is especially the case with instruments such as the cello or the double-bass. I will stress again that, in the unlikely event that a seam opens or worse yet, a crack opens, you should not delay in getting a proper repair done. Proper humidification and consistent good maintenance will allow you to be at ease and concentrate on making beautiful music!
Mark; Hi! I have three H-M guitars with neck re-sets using Hot Hide Glue. I think it’s a huge imveoprment over the rubbery, vinyl Titebond stuff Gibson uses. The Hot Hide Glue actually pulls the wood together as it dries and is very close in chemical makeup to the glue that was used in the `50’s & `60’s. the Titebond results are like placing a sheet of plastic/vinyl between the two pieces of wood and doesn’t allow for a good transfer of vibrations between the two pieces of Mahogany.
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