Larger containers that hold and release more water are commercially available. This humidifier will keep wooden pegs from shrinking and slipping, but only if you don’t practice and keep the case closed. For all other matters, these humidifiers are still insufficient due to the lack of air movement inside a closed case. The humid air is unable to penetrate the f-holes quickly enough to keep the wood in the interior of the violin from shrinking and consequently from cracking.
An efficient instrument humidifier is the one you slip through the f-hole inside of the violin. (“Dampit” or similar products). A “Dampit” is a sponge filled rubber tube with many holes which allow the water to evaporate.
One must be careful when using “Dampits”. The instruction is in the name: They are called “Dampit” not “Dripit”. If prepared incorrectly, one can damage an instrument (commonly the lower ribs of a cello). Additionally, contact between a wet cap (at the upper end of the tube) and the instrument could soften the varnish, causing accelerated wear and a milky finish. Finally, if you always use faucet water, the sponge inside will slowly crust up with minerals and not take more water.
When you wet them under a faucet, there will initially be too much water inside. Wetting the “Dampit” with distilled or filtered water will prolong the “Dampit’s” lifespan. Aside from saturating the sponge, there will be some more water between the sponge and the inside wall of the rubber tubing, which will drip if left as is. It is essential to slide the whole tubing through a towel. By squeezing the lower end of the Dampit with the towel, the sponge inside will be a little under saturated and absorb any free flowing water. Make sure the cap at the upper end, which keeps the rubber tube from slipping all the way in, is dry on the outside.
Some violin cases have built-in hygrometers. They are the first thing people see when they open the case and are impressive. However these $5.00 units are amazingly inaccurate. If you rely on the humidity they indicate you will be in trouble. Don’t look at the number and take it as absolute truth, but look regularly at the dial. For instance if it always shows 80% and suddenly goes to 60% it is time to humidify the violin. You can rely more on the drop indicated by the dial than the actual number.
In Southern California, 50% is a safe humidity for violins that have been here for a few years. If an instrument has come from a humid climate to a dry one, it is advisable to have the upper and lower bouts separated for a few days so they can shrink without risking cracks in the top. After a few days you can have them glued back again. This is important especially for new instruments, because new wood is more hygroscopic and absorbs more water faster in humid climate and also releases it quicker when the weather is dry. For a short visit to a dry climate you can just use a Dampit to avoid problems.
In New York, the humidity in summer is generally quite high. In the winter, when it is cold outside and the homes are heated, the humidity plummets and violin restorers are inundated with crack repair.
Dryness cracks appear in the upper and lower bouts often next to the saddle or neck near the upper or lower edge. In the arched area of the top a dryness crack is less likely. The arch just flattens out a bit to accommodate for the shrinkage.
The flattening of the arch in the center of the instrument results in more pressure of the sound post on the top and back of the instrument. Sometimes, that pressure is so strong that you can feel a bulge in the top at the post area. If you leave this for a long period, that bulge becomes permanent and can sometimes lead to a sound post crack. Of course, there are also sound consequences, because the excessive tightness affects the sound. The more pressure the post exerts on top and back, the brighter or eventually tighter the sound will be. In addition, when the wood has less water content, the sound becomes brighter, sometimes more brittle. With high humidity, the sound becomes darker and less brilliant. The distance of the post from the bridge changes the leverage the bridge has over the post. But, the pressure of the post has more influence on the sound than the distance from the bridge. That the change of pressure is more important than the post position between the f hole and the center is easily demonstrated. We have conducted this experiment numerous times, so you don’t need to spend the money to try it out yourself. Have two sound posts made of the same material, but of different lengths. Put the longer post in a little closer to the center and for comparison afterwards the smaller post further towards the f hole. If the posts are set to exert identical pressure on the top and back, the sound will be pretty much the same.