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ctanzio

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Everything posted by ctanzio

  1. As someone who made a good living analyzing the vibration of many different structures, this article made my head hurt. The primary mechanism of vibration for thin structures is deflection perpendicular to its surface, curved or flat. The sharply curved or "J" shaped saw has substantial restraints at both ends which restricts the deflection of the lower modes of vibration. Draw arrows anywhere perpendicular to the surface and you will see significant components of that deflection which resolve transversely along the sheet to a restrained boundary condition. The gentle recurve which is little more than a flat sheet with a small offset at the ends has no such restraints on deflection perpendicular to the surface. There is no secret sweet spot being discovered at Harvard. If you want a membrane to vibrate strongly, choose a shape whose perpendicular deflections do not resolve into transverse constraints.
  2. Most of the shrinkage of wood at lower temperatures occurs because of the moisture difference between warm and cold air. Shrinkage due to thermal expansion coefficient of the wood is minor compared to the moisture expansion/contraction effects. What you propose would mostly result in mechanical stress cycles. As Don observed, you run the risk of introducing mechanical failures, such as cracking and permanent warping. Meaningful changes in physical properties of materials mostly revolves around exposure to heat above room temperature while limiting humidity. Cycling of temperature and humidity is best avoided. The technical reasons for this is beyond what can be discussed in this forum. But if you want more information, investigate "accelerated thermal aging".
  3. Putting your pretentious drivel and predictable strawmen aside for a moment, all I said was that there was a distinct difference between Taste and Misogyny. It stands unrefuted by your post. Do you believe all beautiful women are capricious? Answer the question. If yes, I have nothing more to say. You have convicted yourself. If no, then why post such an insulting untruth? Oh, and if you intend to use a Latin phrase a mark of erudition, the least you can do is learn the proper form of a gerund in the language.
  4. There is a distinct difference between Taste and Misogyny.
  5. Natural sunlight contains mostly the UV-A spectrum: wavelength 300nm to 400 nm. You can find several LEDs that emit UV light in this range. It is comparable to the UV range of traditional "black lights".
  6. I am certainly no expert on spiccato. But a relaxed grip, especially with the thumb, is all I need to get the bow to bounce lightly, and a slight U-shaped motion of the bow hand. My impressions is that it is quite independent of the type of bow hold one uses.
  7. It is worthwhile to do a search on bow holds. This has been discussed many times and there are lots of videos demonstrating the pros and cons of the most popular holds. There are, and have been, world class violinists that have used all the common bow holds. If one of these holds feels natural and comfortable to you, then that is the one to use!
  8. The thing with shellac is that you do not need lots of layers (i.e, thick) for a smooth finish. Careful surface scrapping after a few repeated grain raisings will give a very smooth raw surface. Seal and conservatively polish with shellac and you can achieve a glass-like finish with a very thin coat. The visual sensation of depth is another matter. But if the wood has interesting grain patterns, then a very thin, transparent coating of shellac can give a great looking finish.
  9. In terms of the frequency of the A0 mode, the science of Helmholtz Resonators both explains and predicts this very fundamental feature of the violin, and can be used to tune the frequency of this mode. The main parameters are the length of the air cavity, the area of the f-holes (or more precisely length of the outline of the f-holes), and the total volume of the air cavity. One does need to exercise some caution in that deviating too much from the geometry, like the shape and placement of the f-holes, one would need to revisit the resonator model and make appropriate geometric shape adjustments. In terms of sound phase and air pumping effects, what is happening depends heavily on which mode of vibration you are considering. It is more useful to think in terms of sound radiation (air movement) through the f-holes as opposed to any difference in phase between the air inside the body and the air outside the body. For most of the sound radiation below 1KHz, air moving cyclically into and out of the f-holes predominates. As note frequencies expand beyond 1KHz, plate vibration starts to take over and air movement through the f-holes becomes much less important. Porting a resonating body will quickly degenerate into a bewildering minefield of different physical effects. One of the simpler engineering challenges tries to make the radiation due to pumping action more efficient. The port opening faces in the direction of where one wants most of the sound to radiate. Violins already have ports. They are called f-holes. Pointing a port opening in any other direction runs counter to making the sound radiation more efficient. However, adjusting the port area and location will shift SOME plate frequencies that are strongly tied to the air modes, and it MIGHT have some effect on the basic air modes. Think of ports in places other than the top as some new form of plate tuning! Have fun with that thread.
  10. Get some Zinsser Amber Shellac and dilute it 1 part denatured alcohol to 1 part shellac by volume. Let it sit overnight in a capped glass jar so most of the wax settles to the bottom. If you want to add a teensy more color to the finish, there are alcohol-based dyes from manufacturers like TransTint. A fraction of a drop is all you need. Reddish-brown tint is good for hiding the scars of paint removal in your case. With a soft brush flow it on fast and thin. Let it dry, about an hour, frequently less. You can try a second coat but shellacs can dissolve previous coats and anything with dye added to it can become streaky. If you get overlap lines, thoroughly dried shellc sands nicely with 800 to 1500 grit sand paper and a light touch. If you do not add dye then the amber color will come across more consistently until the coat gets a bit too thick, then you can get visible melt marks unless you learn how to use a french polishing technique. Another option is any general-purpose spar varnish. Easy to apply and get a smooth coat, but all the wood coloration damage due to stripping will show thru the light orange-brown tint of the varnish. Really not worth spending much time or money refinishing.
  11. My experience with extensive splits along the top in the lower bout is that you need to remove the belly and properly clean and cleat it. Removing a top is not difficult, requires a simple tool, but is a skill that must be learned and exercised with caution. Lots of great youtube videos and websites with picture sequences demonstrating the ins and outs of the procedure. Once you have the top off, you need to clean out the crack. Again a skill that requires some instruction to diagnose the problem and then choose an approach. No special, expensive tools required. After that, in all cases I have encountered, letting the top sit quietly overnight will cause the crack to almost, if not completely, close. There is a logical and scientific explanation for this that I will not mention here. At this point, you are in repair territory that is challenging and requires special tools, supplies and approaches. You might want to do a search on cleating a crack to see if you want to invest the time to learn, and the money to buy the tools and materials needed. For example: hide glue and glue warmer. Gluing the top back onto the ribs poses its own challenges, including tools needed, like a complete set of garland clamps. Good luck!
  12. Thank you for posting the performance. I enjoyed it.
  13. Cremonese violins made before 1800 defy the laws of physics, I guess. Probably the magical incantations and demon rituals Tony Strad performed to make his ground and varnish. Or maybe we are being trolled, yet again?
  14. Thanks for the tests. Is it common for you to have to glue things that have been coated with PVA?
  15. When one asks about the quality of the material, one must also state the specific purposes for which it will be used. This is missing in your questions. A frog has structural purposes: hold the strings securely, slide easily along the stick without wobble, withstand the forces, sweat and oils from the fingers without significant wear. An argument can be made that both frogs you pictured perform all these purposes. The ebony used in one is not superior to the other in this regard. They are equivalent despite the differences in appearance. At this time, and perhaps not so much at the time they were made, appearance is also a purpose. Then the term "superior" becomes a matter of cultural taste and personal preference. Personally, I prefer the look of the frog with the whitish grain pattern. It is infinitely more interesting to me than the second, smooth frog. That second frog looks like a piece of worn, molded plastic in the picture, although it might be more interesting to look at in-person. Now if you are talking about fingerboards, I would have the opposite opinion about appearance. A board with dramatic color variations in grain, or even obvious grain or color variations, is very distracting to me when I play. Yet such ebony may be perfectly fine for strength and wear purposes.
  16. Looks vegan to me.
  17. Nice job on coloring the craquelure. Very believable antique effect. I love the one piece back.
  18. The light absorption of both wood and varnish will noticeably change over time due to normal heat, light and humidity exposure. But care must be exercised when using such a test. How does one perform a light transmission test on a violin that distinguishes between effects due to the wood changes, and effects due to varnish changes or revarnishing and polishing that might occur over the centuries? How does one eliminate a false positive due to the low resistance to aging of some surface/ground treatments? In general, light and UV absorption increases over time in specific bands across the spectrum as wood ages. It is initially very rapid, tapers off, then steadily increases over a long period of time. This may present itself as a noticeable change in color and opacity after a few decades for normal aging, or within a year for extreme weather conditions. Opaque wood would not be a definitive test for a Strad. Only for wood that might be a several decades old due to normal aging. If the changes are not there for a particular violin, it would strongly suggest "new" wood and thus eliminate Strad as a possibility.
  19. Too complicated. For a practical and straight forward approach to reproducing common schools of violin styles, check out Kevin Kelly's site: http://www.kellyviolins.com/design-page.html
  20. There is really no reason to make one's own dyes from raw materials for the ground. Modern synthetic dyes come in a wide range of colors, are color fast, easy and safe to handle, many are transparent, and are available for water or alcohol solvent application. Check out suppliers such as W.D Lockwood, Kremer and Transtint. Water-based synthetic dyes tend to be more color fast but pose challenges when applied to wood due to grain raising. Alcohol-based dyes are easy to combine with diluted shellac to make a colored ground/sealer. But I found that this layer has to be "sealed" with an oil-based varnish if one wants to use an alcohol varnish as the top layer.
  21. Saffron as a dye for varnish/ground/sealer gives a brilliant yellow color that, sadly, fades within a year from my personal experience. Used as a dye for fabric, the mordants used to fix the dye to the fibers might extend the color fastness, but I never pursued to option for wood working.
  22. Davide, thank you so much for sharing your expertise. Your videos are a fabulous resource.
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