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The Effect of Finishes on the Vibration Properties of Spruce Guitar Soundboard Wood

I read an interesting paper recently published in the Savart Journal which is published in collaboration with the Guild of American Luthiers.

The article was written by Howard P. Stephens, retired from Sandia National Laboratories working as a materials research and R&D management engineer.  He received his Ph.D. from Purdue University where he was a National Science Foundation Fellow.  He also served as a Division Chair of the American Chemical Society and as a Technical Advisor to the U.S. Department of Energy, Office of Basic Energy Sciences.  After retiring from Sandia, Howards returned to his interest in Luthierie applying his scientific experience to researching plate vibrational properties and is a member of the Guild of American Luthiers.

The paper presents a study of the effect of a sealer and four finishes on the vibration properties of spruce for guitar soundboards.  Two fo the finishes, de-waxed shellac (used in French polishing) and nitrocellulose instrument lacquer, are evaporative finishes, traditionally used for guitars.  The third and fourth finishes are reactive shellac-based finishes.  

The study measured the fundamental vibrational frequency and damping quality factor of Sitka spruce test bars coated with sealer and finishes.

Statistical analyses showed that all of the top coat finishes cured for seven weeks were equivalent with respect to their effect on the vibrational properties of the spruce bars.

I found the results very interesting; making me question the strength and hardening effects of the four different finishes.  I know that nitrocellulose lacquer which is typically used on archtop instruments is constantly curing even after many, many years of its application.  I don’t find it to be very hard and scratch resistant but I do think it’s better than straight shellac.  I am also not fond of the health, smell and environmental issues related to nitrocellulose lacquer.  Its nasty stuff!

I have used nitrocellulose for several guitars but wanted something safer, healthier, and harder than either shellac or nitrocellulose for my instruments.  I researched and tested several waterborne lacquers; some designed specifically for musical instruments and some over-the-counter products.  As a result of my research, I have settled on a new waterborne lacquer that sprays thin and smooth, lays down evenly, and is very hard after curing seven days.  It is much safer for my health and the health of the player of the instrument.  

This was a very helpful paper and led me to discover the new waterborne lacquers on the market of today.  Today’s waterborne lacquer is much better than those of previous years, in my opinion.  It is harder, more scratch-resistant and ultra-clear compared to previous versions.  

 

 

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