(This is an experiment conducted 9 years ago.)
This is an experiment to see how the color changes when wood is exposed to UV light. Experiment up to 600 hours in 100-hour increments to find the most suitable time.
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Various methods are being tried for ground coloring (Sottofondo) of wood before varnishing a violin. Methods such as directly applying pigments/dyes to wood and chemical methods such as applying sodium nitrite (NaNO2) and then exposing it to UV are widely used. Considering the completeness of the results, I conducted this experiment because I was not yet able to obtain satisfactory results.
The common problem with the above methods in my opinion is that satisfactory colors cannot be obtained, and additionally, the pigment/dye method has the problem of requiring solvents (water, alcohol, etc.) to be applied directly to well-dried wood. In addition, the NaNO2+UV method has the problem of producing different colors depending on the type of wood (maple, spruce), and the color saturation is expressed differently depending on the degree of application of NaNO2. There is even a problem in that areas where application is accidentally missed remain white.
No matter what anyone says, the most beautiful and natural color of wood is the color of wood that has naturally discolored over a long period of time. It is mostly caused by ultraviolet rays from sunlight, and in some cases, various types of pollution may also be a cause.
In this experiment, I will examine the change in wood color solely due to UV. The purpose of this experiment is to check how the color of wood changes from 100 to 600 hours, and find out the most reasonable exposure time.
1. Experimental equipment
Test pieces : maple piece * 7EA
UV-A lamp: 40W 1EA + 6W 2EA
UV-C lamp: 36W 1EA + 6W 2EA
2. Experimental method
Place one test piece in a box away from light and store it.
Put 6 test pieces into UV-Box and start light exposure.
After 100 hours, take out one test piece from the UV-Box.
After 200 hours (cumulative), take out one test piece from the UV-Box.
...
After 600 hours (cumulative), take out one last test piece from the UV-Box. (UV-Box off)
Place 7 test pieces (exposure times 0h, 100h, 200h,..., 600h) in one place and compare colors.
3. Results and Discussion
There is a big difference between 0 hours and 100 hours, there is no big difference between 100 hours and 200 hours, and a small difference is visible between 200 hours and 300 hours. After 300 hours, change is very slow.
Looking at the resulting photo, the color at 500 hours is darker than at 600 hours, which is presumed to be a result obtained because the texture is slightly different for each test pieces. If judged from the above, it can be said that photodiscoloration by UV is almost completed in 300 hours.
Since it is a one-time experiment on only one set of test pieces, it is difficult to say that the results are general enough, but it is expected that these experimental results alone can be sufficiently applied to musical instrument work. One regret is that it would be more helpful if there were more precise results between 200 and 300 hours.
In terms of efficiency, less than 300 hours seems appropriate when working on an actual instrument, and when time is insufficient, some effects may be achieved with about 100 hours. If more lamps are used than the UV lamps used in this experiment, the time can be further reduced. As the number of lamps increases, the temperature inside the UV-Box increases and the humidity decreases, so when applying it to an actual musical instrument, countermeasures (fan, humidification) will be necessary.
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