(edited 8/2014)
Effect of Sunlight (ultra-violet light) on violin plates...
...After much experimentation and testing, I would sugges that although UV (sunlight) exposure does change the surface coloration (gives the wood a pleasing sun tan), and does have an effect on the overtones heard with tap tones; I beleive it actually has little or no tap tone effect; that is, the base note of the heard tap tone remains the same.
...By using sunlight or UV exposure to darken the surface wood, it might bring about the final external coloration sooner.
The above two photos show the plates of my Opus # 20 violin before U.V. exposure...
The two photos show the same two plates after two weeks U.V. exposure (24/7)...
... Even the inside of the plates can be 'tanned' in this method...
Bulb information: General Electric 24", 20 watt # 10244 / F20T12/BL
Marked on bulb: F 20 T 12-BL / Black Light / 20 watt
Purchased from www.Granger.com
part # SV 871-8
Ground Coating (outside only)
...If only one surface of the plate is treated, distortion may occure. Be sure to have a pan of water nearby to keep moisture in the wood during UV treatment.
..If you do nothing, it will still darken over the years due to indirect UV exposure, and perhaps have less stress, long term....Just a thought.
Cross section of wood strip being tested, 0.100" thick spruce [quarter sawn], showing distortion after drying and U.V. light exposure.