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Dependence of Vibrational Properties of Wood on Varnishing during Its Drying Process in Violin Manufacturing

The influence of varnishing for violins on the vibrational properties of wood strips was investigated during the drying process by vaporization of solvent. The changes of weight, specific dynamic Young's modulus (E/r), and loss factor (tan δ) by varnishing with natural varnish (shellac) and artificial ones (cellulose nitrate: CN) were measured and their subsequent changes were traced for 1 to 2 years. For both varnishes, though the remarkable weight decrease just after varnishing ceased after 3 to 5 months, a slight weight decrease continued even after then. The change of E/r became almost undetectable within several months, whereas the decrease of tan δ continued for a longer period. Acoustic converting efficiency (ACE) fell down drastically just after varnishing, but it recovered extending for 1 year. The recovery of ACE was more largely for shellac varnished specimen than the CN lacquered one. The frequency dependencies of E/r and tan δ changed by applying the CN lacquer, whereas those by shellac varnish did not change significantly. These results suggested the superiority of shellac varnish to CN lacquer