It starts with mature, old growth trees and then requires a long time of natural drying. With stringed instruments such as violins, age is an advantage.
Much is made of the fine violins made long ago. The names Stradivarius, Guarneri, and Amati immediately come to mind. The ages of those 16th, 17th and 18th century violins (and violas and cellos) only seem to increase their value, suggesting that time is no enemy of fine stringed instruments.
Time is also a quality ascribed to new violins. How so? Wood that is specifically harvested in the cold, dormant seasons is cut and stored carefully and left to age before the violin makers touch it. Some of the stacks of raw wood inventory are kept on hand for as long as 50 years.
Which begs the question: What does aging do to wood that, one assumes, improves the quality of the violin, cello, and viola? The porosity of the wood and its hygroscopic nature – hygroscopy means the material (the wood) attracts and holds water – mean it needs time for that water to leave. For products such as wood furniture and wood building materials, kiln drying sufficiently removes the moisture. But kilning changes the cellular structure of the wood, which is not good for a musical instrument because it adversely alters the acoustics of the instrument.
The woods used for violinmaking are usually spruce and maple, spruce for the top and maple for the back. For both, harvesting is done with old growth trees (again, age is an advantage), grown at high altitudes on north slopes where conditions create denser wood (the Stradivariuses are believed to have been made from trees that grew during a mini-ice age in Europe, when growth was very slow and the wood was therefore more dense). Once felled, the wood is cut into cylindrical shapes, or sliced into wedges (“billets”) that are slightly bigger than the finished pieces. They are sealed on the ends but left exposed to air on all sides to allow the slow drying process.
The woods for making cellos, violas and string bass are typically made from maple and spruce as well. And the acoustic characteristics of aging apply to these instruments also.
Not every violin is made through such a painstaking process involving long ago-harvested wood. Clearly, it is less expensive to use newer wood dried by different methods. And those savings are passed on to buyers – students, and less serious players. But it also explains why better quality violins, made by more skilled luthiers, cost more.