Thanks Ray for this detailed explanation. I do, now, understand why coming back to my dry home from the lutemakers relatively humid atmosphere could have caused the initial crack, but also why local rehumidification by a "snake" might have worsened the situation, rather than improve it. Any change local or otherwise), in whatever direction can be a problem. Although the person who advised me to use the snake, has used it on all his lutes, without ill effect.
> In the piano trade, we have the Dampp-chaser. This is a name-brand > humidity control system designed for pianos I will make a search on this damp chaser, but it sounds more as though it removes humidity, Here it is more a problem of increasing it. I imagine this thing will be rather expensive and perhaps large. Do you have any details? I remember a lutist years ago telling me he would simply increase the humidity by releasing the steam of a pressure cooker, but I have been told that is not really a good solution. I have managed to raise humidity levels by filling the bath with hot water, but that is not a very ecological solution, unless you actually take a bath, at the same time. Regards Anthony Le 18 sept. 07 à 14:13, Ray Brohinsky a écrit : > I have generally kept out of this discussion, but there are some > things that seem to need saying, all in one place. I can't guarantee > that everything I'm saying here is new information (blame low-quality > short-term memory if it isn't.) > > Humidity is a function of water-content and temperature when we're > talking about air. This means that any discussion of the effects of > humidity on wood needs some basic qualification right from the start. > Where you live (i.e., your climate) has a gigantic effect. If you live > in New England, humidity control is a given. If you live in Arizona, > humidifying an instrument may be utterly fruitless. > > This is because the climate of New England varies, seasonally and > day-to-day, but Arizona is dry pretty much year-round. One thing that > attests to this is the story of a master piano technician who showed > me some of the ropes: he'd lived all his life in Arizona, and tuned > each piano about once a year. When he came to Connecticut, he found > himself tuning similar pianos (there's no such thing as two identical > pianos) as many as four times a year, once for each season. In New > England, the air tends to have a large amount of water in it, year > round, but in the heating season (which wraps from early in Fall to > late in Spring), cold moist air, drawn into a house and heated, drops > in relative humidity. Relative humidity is important because that is > what wood responds to. > > In the piano trade, we have the Dampp-chaser. This is a name-brand > humidity control system designed for pianos (which grew from an idea > the inventer came up with to keep the insides of radios he maintained > in Africa from corroding, and later applied to cedar closets in > Florida.) The system consists of a heater, to drive rel humidity down, > a warm-moist humidifier, to drive rel humidity up, and a humidistat, > to monitor the relative humidity and ensure that it is maintained > within the affected space to a 5%-20% range, regardless of the room > humidity. Up here in CT, adding one of these systems to a > humidity-ravaged piano is like magic: pinblocks tighten up, improving > tuning stability, seasonally-affected-actions even out and can be > adjusted once-and-for-all (all meaning, in this case, for as long as > the owner keeps the system plugged in and water in the reservoir!) > > One technician who was in a position to make some tests reported that > in dead winter, with a pair of humidifiers running in the piano room, > it took about a minute after the humidifiers shut off for the relative > humidity in the room to drop from ~45% to lower than his meter could > measure (around 5%). That is because there is nothing, in a "normal" > room, to stop communication between the air in the room and the air of > the rest of the house. I know I was surprised to find out how quickly > the humidity of a treated space changes when the area around the > enclosure has access to it. > > For upright pianos, the insides are sufficiently enclosed that, as > long as the top is closed, the insides can be regulated well over the > entire space. For grand pianos, with the soundboard exposed at the > bottom side, the space (as much as five inches) between the sound > board and pin block, and the fact that the "box" is habitually open if > the desk is up, it's almost hopeless, but some good comes from closing > off the bottom of the piano with a dense-gauze cloth cover. > > How does this relate to lutes? > > Well, first of all, the surface of a lute can be exposed for short > periods of time (as much as days) to various humidity levels without > the wood automatically assuming that level. If the lute is exposed to > a humidity level significantly different from the starting level in > the wood for "enough time", then the wood will shrink or swell, and if > the changing dimension is anchored at the ends, will split, crack, bow > or warp. I don't know what relative humidity level is maintained in > any specific luthier's shop, but it'd be good to find out, and take > steps to maintain a lute at that relative humidity. Getting it back to > that atmosphere will return the lute very closely to its original > condition if it hasn't been too dried out or over-humidified (i.e., if > the lute hasn't sustained damage that requires repair.) > > The wood in a lute is cut to a shape, bonded into the lute, and most > often, further shaped. If done well, the result is a balanced system > with stresses worked out of it. As long as nothing happens to change > the dimensions of an individual part of the lute faster than other > parts, things should stay as it was built. The thing that changes wood > with the longest-lasting effect is humidity, and the general rule is > that cold will make things change but returning the instrument to the > original temperature will bring the parts back quickly to their > 'original' sizes, but a humidity change affects different parts of an > instrument differently (based on composition, shape, etc.) and just > restoring the instrument to the same humidity level will not > immediately restore everything. Humidity generally gets into wood > faster than it gets out. Either way, once a lute enters a new climate, > it will change from its initial condition, with stresses being formed > where different parts react differently to moisture. When these > stresses exceed the bond strength of the adhesives, parts will break > loose. Where it doesn't, but does exceed the wood's internal strength, > cracks will happen. Where stresses don't rise to the breaking point, > they can still cause bulging, etc. > > This is why _not_ taking efforts to humidify a case in a dry climate > can lead to wood cracking and splitting, and why _going too far_ to > humidify a lute can cause splitting and cracking. > > I do not know of a controlled humidification system for any instrument > cases. It would be hard to make, hard to get to work well (because > there is so little room in the closed case for air to be shoved around > to get a good homogeneous atmosphere throughout the case), and > horribly expensive. The heater part would actually be pretty easy to > do, especially with adhesive-backed sheet heaters), but the > warm-humidity generator would be a real bother. The electronics would > seem to most an unwelcome intrusion, along with the extra weight of > the system, and the water reservoir... well, just try flying with a > case like that! > > Anyway, if you are worried about the fate of your lute, in case or on > wall, this is what I'd suggest: First, ask the luthier (if they are > still alive) what humidity they keep their wood stored in. Then: in a > case, have a battery-operated humidity sensor, and look at it every > time you open the case. That'll be as close to the steady-state closed > case humidity as you can get (short of the remote-sensing approch > Anthony Hind mentions). Figure that the meter is guaranteed to be off > by +/-3% if it's expensive, +/-5% otherwise. The absolute measurement > isn't really so important as keeping the level the same. So, if you > open the case and it's 15%, use a humidifier (snake, > pumice-inna-snuffbox with holes, damp washcloth in a plastic bag in > the accessory bin, etc.) If it is 50% or higher, consider leaving it > open in a room with a dehumidifier, where the doors are closed, and > monitor the room. > > If you hang the lute on the wall, put the humidity meter very close to > it (as close as aesthetics will allow, or closer if you're a _real_ > aesthete!) and keep an eye on the room humidity that way. Again, if it > is low, humidify. If it is high, dehumidify. In either case, use the > meter to monitor humidity _near the lute_, because humidity over by > the de/humidifier isn't going to be the same. > > I hope this is helpful! > ray > > > > To get on or off this list see list information at > http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
