Effect of Sunlight (ultra-violet light) on violin plates...
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...
...This is a view looking down into my U.V. exposure box that I built. Notice the two plates hung inside and the pan of water in the bottom which keeps the plates from drying out from the 100 degree F. heat. Two special 40 watt U.V. generating fluorescent bulbs (2 feet long) simulate continuous sunlight.
...Notice how the inside of the box and lid are lined with aluminum foil glued in place, to direct the light evenly around inside and make sure it is absorbed by the plates and not by the inside surfaces of the box!
Ground Coating (outside only)
Cross section of wood strip being tested, 0.100" thick spruce [quarter sawn], showing distortion after drying and U.V. light exposure.
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
...After much experimentation and testing, I would suggest 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, (and look better also!)
...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.
..So... If you are using a ground coating such as Propolis (before the varnish coats), be sure to use it equally on both inner and outer sides of the plates and ribs.