Oh, and on the topic of bows, look up weather sticks. 

The violin bow is usually hardwood which will react less than fir or birch, but at least extremes of humidity one way or another might possibly cause a bit of warp or twist that may only be there when the stick gets very dry or the weather is very humid.  Just a thought.

@RU: Yeah, homeostasis isn't quite the right word, but it was what comes to mind since the way the processes are functioning seem to me to possibly be more complex than a simple equilibrium and the parts involved may still function somewhat as they did when part of a living organism.

We can agree that a piece of wood used for a violin or bridge is dead, within our usual manner of thinking.  But the way water moves in and out will still work through cell walls, and the capillaries in even a piece of aged hardwood will still take up liquid in a fashion reminiscent to a live stalk of celery.  Slower and more a passive process than the wood had in life, but I think it may be part of what gives wooden instruments like the acoustic violin some of their unique properties.

But yes, homeostasis might imply the parts of a living organism to some folks.  I was thinking more in terms of it's literal "homeo=same, stasis=standing" sense, and used it because I am beginning to suspect the process is a bit more complex than say a pile of salt with a certain amount of water in a sealed container, which will reach equilibrium after a certain amount of time.

Agreed, though, that it may not have been the best choice of terms.

The finish, for that matter (depending on what sort of finish was used) may also be somewhat permeable.  Oil finishes allow both water and air to affect the wood, though much slower than with unfinished wood, and spirit varnishes which are organic resin dissolved in a solvent base also will still allow some effect from humidity and atmosphere even though it will be much slower than on unfinished wood.

The "sealer" also may be mostly gelatin (hide glue), which is not entirely dead/stable in the same sense as say, a PVA "white" or "carpenter's" glue (vinyl).  That it still is somewhat hydrophilic and will tighten and relax slightly with changes in moisture and temperature may be something that actually helps keep together an instrument made of materials and finish similar to what were used a century or more ago.  

But that is largely just "wondering", and such matters are outside the scope of most players' interests.  

Besides, in this particular case, I don't really have any idea what the finish of my violin is.  The more expensive Hoffmanns I think are oil varnish, but mine is the bottom of the line and might be anything from something purely synthetic to a mixture of Chinese water buffalo snot and yesterday's tea. LOL 

A properly traditionally finished violin, though, the finish itself would react to changes in humidity to some degree, and would also be at least a small part of the puzzle.

Umm.. we now return everyone to your normal entertaining and musical thoughts..

I'd say that by now, the humidifier and case have probably stabilized about as much as they are going to.  It holds pretty steady in the low end of 40%, with current climate and weather.

However, on the advice of some folks, including Fiddlestix earlier in this thread, I also got some humidifiers for the house.  Nothing fancy or new-fangled, just three old "warm mist" type humidifiers that were going very cheap at a second-hand store.  I paid less than 10$ for the three of them altogether.  They go through over a gallon of water a day each, and the house humidity has been holding pretty steady at around 40%. 

I was advised to consider any "in-case" humidifier as being just a bit of insurance and not to think of the case as a sealed environment like a space station or something.  And to not count on the case too much, since the materials it is made of just aren't all that good for maintaining an instrument so far as conditions like humidity are concerned.  An in-case humidifier or using a "vapor vial" or whatever can be useful to moderate extremes and sudden changes while the instrument is in the case, but shouldn''t be looked to as a 100% solution.

Most inexpensive modern cases are made of basically closed cell foam, covered with some polyester canvas and lined with some sort of soft acrylic plush and a bit of foam rubber in there somewhere for padding.  That makes them excellent for protecting the instrument from typical banging around and temperature changes, but not so good for humidity. 

Somewhat nicer cases usually will have a wood shell (at least thin plywood), maybe leather over that, and be lined with some variety of natural fibre cloth or in some cases soft suede leather.  Those materials all add a bit more protection and will help hold humidity stable to some degree.  Synthetic materials can have many good design points, but most of them don't absorb and release water vapour like some natural materials do. 

I'm not quite up to the notion or relining the case or building a new case just at this moment, so another project on my list will be to make a bag out of most likely silk to keep the violin in when it's in the case.  That's not too tough a project and would be less work and expense than buying or building an entirely new case. 

But back to the humidifier.  I think it does help a bit.  No huge miracle, but a bit of extra "insurance" that can help protect the instrument in dry weather.  Certainly worth a little time and a few bucks, but nothing where I'd advise running right out and spending a lot on an expensive one.  The hygrometer is probably actually more important, so one can see what the humidity in the case is.  Those can be gotten inexpensively as well.

Where I think that keeping the instrument in a better and more stable humidity range helps is that the sound seems more consistent.  Subjectively, I would also say the "feel" and "playability" of the instrument are enhanced by keeping it from getting too dry.. But that is such a subjective sort of observation that I don't even know how I'd go about showing it qualitatively. 

Bottom line, I like the in-case humidifier and feel it was well worth the couple bucks I spent on the project.  So it might be worth a few bucks more to come up with something a bit nicer looking.  But I wouldn't run out in a panic and spend the rent money on a fancy one.

Hi Steve. 

It's easy.  A mixture of salt and water will reach a certain equillibrium.  It varies depending on what salt is used, but for common table salt (NaCl), the point will be about 75% humidity.

So you take a small container, teacup sized or smaller, let's say.  Fill it up about halfway with salt, and then add enough water that the salt is damp, but not completely dissolved.  A "slush", basically.  Put that into an airtight container with the hygrometer(s) you want to test.  After 12 hours or so, the humidity should read close to 75%.  If you use a *large* airtight container, it might take longer than that, but when readings are stable for more than a couple hours at room temp, you pretty much have to be at equilibrium. 

It may be a couple % off, so not "lab grade", but definitely close enough for most purposes like this.

You really only have to do it with one hygrometer, and then you can use that as your "reference" that you set the others to match after they've been near it for an hour or so.