...What I would suggest before doing this step, is to expose the violin plates to natural sunlight over a period of a week or so and carefully monitor to see if the plate tones increase. If they do increase, continue this exposure until both plates (front and back) no longer change. Then the tap tones you adjust to will not change from these effects in the future.
...You want the back plate to be even all over and 3/4 of a full tone higher than the top plate ( 1 1/2 semi-tones); {a semi-tone being the distance between any two adjacent piano keyboard keys, that the interval between a black key and a white key}.
...You want the top plate to be even all over and the bass bar to exactly match the plate through out its length. (the exception is the sound post pad which should match the tone of the back plate.)
...Use 322 HZ for the top plate and 353.5HZ for the back plate and adjust up or down to this goal.
...If you want to lower the tone of the wood in a certain area, make it thinner.
...It will be obvious that it is easy to remove wood and very difficult to put it back on again, so be careful! It is better to work slowly and approach your goal frequency in small steps than to try and do it all at once.
...The edges thickness is to be maintianed, and the plate wood across the ends of the plates inside should not be removed (leave it the same height as the edges for strength.)
...Complete the graduation scheme on the plate you are working on, (in my case as shown in the above photo, I continue working until all the black spots just disappear). Then we are ready to make our adjustments towards our goal frequency. Remember that if we are working with plates with fully mature varnish/ surface (exposed to enough U.V. light so that they no longer increase in tone) the adjustments we make now will be 'permanent'. However, if we are working with new plates (probably unvarnished and with no ground coats or U.V. exposure, we must leave our plates at a frequency lower than our final 'goal' frequencies of 322HZ top plate and 353.5HZ back plate, enough to allow for future increases in plate frequency (pitch or tone) to reach our goal frequencies.
...With the violin I recently completed [my opus # 20 violin], based on tests on samples and experience, I estimated that the plates needed to be adjusted to beginning frequencies of 224HZ top plate and 256HZ back plate (leaving the sound post pad on the top plate to 248HZ).
...Eleven days (24 hours per day) in my U.V. light box with the plates hung vertically (ribs glued to the back plate but the top plate not yet glued on, so the U.V. light is absorbed equally by inside and outside surfaces) raised the plate frequencies to 264HZ top plate and 296 HZ back plate.
...At this point the wood had darkened to a pleasant 'suntan' color and had stopped increasing in frequency.
...After the body was glued together (after 1 1/2 days in a desiccant drying bag to reduce plate moisture.. see separate article) I brushed on a full coat of my preparation coating #A (... see separate article on preparation coating formulas), a mixture of minerals and hide glue and water, and then seven coats of propolis containing Eurpoean oil varnish (over a four day period). I then hung completed body back in U.V. box (with a pan of water in the bottom to prevent excessive drying out) to 'develop' the preparation coat. After four days the plate frequencies were 328 HZ top plate and 355 HZ back plate.
...Next I hung completed violin outside under the eave of my wood shop, exposing the violin surface to direct morning to noon sunlight and bright but indirect sunlight until sunset each day for seven weeks.
...At the end of this period of time the plate frequencies were:
320 HZ top plate and 352 Hz back plate.
...I then sanded the varnish surface level and sanded {up to # 12,000} and then polished the varnish until ready for use. The plate frequencies then were:
318 HZ top plate and 343 Hz back plate. Another five days in the sunlight raised the plates to my goal frequencies of 322 and 353HZ. (I alternated back and top toward the sunlight until goals were met.) {Be sure to cover the ebony fingerboard with aluminum foil to keep it absorbing excessive heat and warping}.
...All this work is unfortuately necessary to achieve our goal for the plates of:
stable frequency plates, each even all over in tap tones, with about 1 1/2 semi-tone plate separation {that is: 3/4 of a whole tone}. This plate tone is however, foundational to the sound the instrument will make over it's long life, and since it is not easily changed, might well be worth some time and effort to do correctly.
