Why does wood crack?
Wood, being a material that was once very much alive, and quite full of water, never loses its ability to absorb moisture from its surroundings. When it does absorb water, it expands and when it dries again, it contracts.
Temperaturehas an effect on wood, but moisture has more effect on it. Extreme heat will cause the moisture to evaporate and thus the wood will shrink rapidly. Extreme cold causes moisture to expand and in turn causes the wood to expand as well.
Wood cracks when it expands or contracts too quickly or unevenly.
How much does wood move?
The ancient Egyptians used this discovery to their advantage. One method used to mine great stones to build the pyramids was to put dry wood wedges into cracks in the stone and pour water on them. As the wood expanded it would continue to crack the stone and eventually separate it. Studies have found that in some wood this water expansion can develop as much as 4,000 pounds per square inch of pressure. To give you an idea of how much pressure that is, think of it like this: Put your left index finger under a ¾” board 12” x12”. Now with your other hand, stack 192 midsized cars end to end on that board. Imagine the pain. That is what is going on inside your instrument every time it is played. No wonder they crack.
What can I do?
· Expect it to crack sooner or later, as it is wood!
· Take precautions
Don’t keep wood instruments in extreme cold (car in winter) or extreme heat (car the rest of the year) conditions. If your instrument is by chance exposed to the cold, once you bring indoors try not to open case completely. Rather lift the top of case just enough to put a pencil between the openings at the end of the case for about 10 minutes. This will allow the instrument (wood) to gradually come to room temperature without extreme stress on the glue joints.
Heat will also cause a problem. Instruments left in trunks or vehicles on hot days may cause the instrument to dry out causing cracks or the separation of glue joints may occur. It is good idea to consider purchasing a Dampit in order to provide humidity for your instrument.
Loosen the bow. Extreme cold or heat may shrink the horse hair and cause it to break or pull out of the (frog) grip.
Rosin is made from tree sap. Rosin will become brittle in the cold and possibly melt in the heat.