How great is the danger of the wood
Studies performed by the Institute for Musical Instrument Making in Zwota/Vogtland - involving experiments using wood up to 40 years old - confirm that a seasoning time in excess of eight years does not reduce the danger of cracking if the wood does not otherwise receive the necessary treatment and care.
Wood adapts naturally to the local climate. It is hygroscopic, i.e. in changing environmental conditions it absorbs or releases moisture, whereby it has built-in protection in the form of oils and resins stored within it. During the course of flute-making the wood is additionally impregnated, though in spite of everything this process cannot totally eliminate its hygroscopicity.
It is thus impossible to offer a guarantee against the wood cracking!
Good, careful maintenance of the instrument is thus the best precaution against cracks.
The player's breath exposes the flute to constantly fluctuating moisture and temperature levels, and condensation forms. This leads to swelling of the inner bore of the flute; the dry exterior does not yield, and in extreme cases this can result in superficial cracks. In such cases people tend to think that the wood used for the instrument has not been sufficiently dried out. But this viewpoint is incorrect, as experience has shown that cracks do not occur on the surface of wood which is still moist, but rather that shrinkage or drying result in the loosening of rings or other metal parts fixed in the wood.
Cracking in the wood surface is thus not a quality defect of the wood but an indication of its having been carelessly treated.
The danger of cracks forming should be neither under- nor overestimated. In the case of oboes and clarinets wood has become generally accepted in preference to metal or plastic, and players are happy to take a modicum of extra maintenance work into the bargain in return for a more beautiful timbre.
The body-wall thickness of clarinets is approx. 8 mm and that of oboes approx. 6 mm, whilst that of my flutes and piccolos is only approx. 3 mm. The difference in tension is thus considerably less in flutes than in other woodwind instruments. And the different method of tone production is to be taken into consideration in comparisons - in flutes the airstream splits on the edge of the embouchure hole, and only around half of it enters the instrument.
The danger of cracks forming in wooden flutes is thus considerably less than in other wooden instruments.