ctanzio

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About ctanzio

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  1. ctanzio

    Stradivari's secret was a concept?

    What are the odds that the player has significant hearing loss from playing a loud instrument at maximum power for many years? Just suggesting that claims of a violin being quiet under the ear but powerful to spectators in a hall may be something that can only be accurately measured by a researcher, not a player.
  2. ctanzio

    Cello edge not lining up

    Cracked instruments that are strung at tension for an extended period of time can exhibit strange miss-alignments due do plate deformation caused by creep in highly stressed areas of the plate. Sometimes placing the plate on a flat surface for a few days and gently clamping a few edges to get it to sit flush will reverse enough of the creep to correct the alignment issues. You can also try carefully heating the clamped plate with a hair dryer, or carefully moistening the underside before clamping.
  3. ctanzio

    Varnishing with spirit varnish (sealer?)

    More plaster than water. Two cups of PoP to one cup of water will turn the plaster into a solid clump. So you want to start with much less PoP per cup of water. Rather than bore you with solubility calculations, start with about 1/4 cup of Pop per cup of water. Shake vigorously. Let it stand for a bit. If very little material settles out, add another 1/4 cup and repeat. At some point most of the plaster will start to settle to the bottom and no more will dissolve in the water. Transfer the water to a clean jar and discard the plaster that settled to the bottom. Now filter the water to remove additives and impurities, probably mostly fine sand. The filtered water should appear clear. If you test the pH of the water with litmus paper, it should have a neutral pH. If there is a lot of undissolved plaster floating in the water, I believe it will test slightly acidic. When you wipe the saturated water onto a surface, the calcium sulfate will form a very fine, white, powdery coating as the water evaporates. Under a microscope, it should appear as very fine crystals that are typically smaller in dimension than the average size of the porous sections of wood grain. With repeated application, the calcium sulfate crystals will fill the porous grain and start to cover the surface of the wood. Covering it with a thin coat of diluted shellac will make the calcium sulfate transparent. Be careful not to confuse plaster of paris with lime plaster. These are two different but common materials. Lime plaster releases a lot more heat when combined with water and can be corrosive to the skin. There is the question of how hazey a coat of PoP should be applied. I think Roger Hargrave's practice uses a very pronounced white hazey coat to control the application of an intensely colored oil varnish.
  4. ctanzio

    The Sound of Stradivari - Patrick Kreit

    Without a clear, widely accepted model of what the vibrational details of a world class violin looks like, it is hard to justify the time and considerable expense needed to gather relevant data. In the world of applied physics, we would only pursue this approach if there was some extreme performance goal we were trying to achieve and someone willing to fund the design approach, usually government or a consortium of companies. There is a lot to be said for figuring out what works by trial and error, then carefully controlling the quality and properties of the materials and the dimensions of the finished product. If one relies on frequency data and does not consider relative amplitudes and damping, then sure. Here is a question: Suppose I carefully control my wood selection by, say, damping and sound speed. These are easy to measure and cover the physical properties which dominate vibrational effects. If I now carefully control the dimensions of the plates and the quality and amount of varnish applied and get "good" results, is it reasonable to say the following two things? 1. If I make another violin with the "same" wood properties, dimensions and varnish, isn't it reasonable to expect another "good" result? 2. Wouldn't one expect the frequencies of the dominant vibrational modes to be the same between the two violins? On a related matter, I have studied manipulations of violin sounds where the sound is passed through a filter that reduces or amplifies the frequency components associated with some fundamental modes. The results are cited as "proof" that these modes have small effect on the tone of the sound. This is not technically correct. If one imagines the violin as a set of harmonic oscillators that are excited by a vibrating string, the suppressing or amplifying a frequency component of the combined sound is NOT the same as suppressing or amplifying the response of the single oscillator that has that frequency. So these types of tests have to be approached with some caution.
  5. ctanzio

    Varnishing with spirit varnish (sealer?)

    I have used saturated/filtered solutions of Plaster of Paris and water as a ground/sealer. Two to three coats lightly wiped or brushed on. Let each coat thoroughly dry before applying another. It will built up a uniform haze. Pay special attention to end grain areas. I apply two coats of diluted, dewaxed blonde shellac to turn the PoP haze transparent, although orange or ruby shellac will also work well. The surface is now ready for color/finish varnish. The grain will raise a bit between coats of the PoP due to initial the water absorption if you did not pre-raise and scrape the surface before applying the PoP. This is not necessarily a bad thing unless you are going for a smooth French Polish type of finish.
  6. ctanzio

    The Sound of Stradivari - Patrick Kreit

    There seems to be two main claims made: 1. There is something called the "Stradavari Sound", and 2. Frequencies of open plates can be used to predict the performance of a finished violin. On the first item, there has been considerable contentious discussion on this forum on whether or not there is such a thing as a "Stradavari Sound". Personally, I am unconvinced, having heard a variety of Strads over the years that shared no commonality of tone quality other than being very loud. For example, I wonder how more sublime the playing of David Oistrakh would have been had he made a career with Oscar Shumsky's tonally rich Strad instead of the screechy Strads made available to him. On the second item, there is a good scientific basis for using plate modes under one condition (open plates) to predict performance in another condition (finished violin). However, it requires an "adequate detail" of the modes to be understood and reproduced. In the engineering world, the approach has been used for years to successfully design structures for use in the military, power generating, structural and aviation fields, to name a few. There are four areas that engineers seek to understand to achieve "adequate detail" of the vibration. - mode frequency: When a plate is subjected to a simultaneous full spectrum of vibrations, it will vibrate most strongly at certain frequencies called modes. This is the main (and sometimes sole) focus of plate tuning approaches. They usually take to form of tapping in the plate and recording the knocking sound. A Fourier Analysis of the recorded wave form will reveal which frequencies are most prominent in the plate's response to the tap. When the plates are glued to the ribs, the mode frequencies will change in reasonably predictable ways. - mode shapes: This is how the plates deflect at each frequency. Plates are typically mounted horizontally above a speaker and dusted with salt or other light, granular material. The speaker is then fed a sine wave at each of the frequencies identified in the previous step. The grains will settle where the plates move the least called node points, lines or areas depending how much of the plates fails to deflect. The shapes formed by the grains are called "Chladni Diagrams". The detailed mode shapes of the finished structure are more difficult to predict across the whole spectrum of "open structure" modes, but there is usually a subset of shapes that can be reasonably predicted. For example, you can find Chladni diagrams of the major open plate modes for a violin all over the internet. These shapes will look similar among all the violins, but hardly exactly the same. But small variations in shape can have a profound impact on how energy is transferred to plates by excitation mechanisms, like the bridge/post in a violin. - modal participation: This is how much of the violin's mass is involved in the vibration. This is roughly related to how much power the violin can generate at a frequency. It is normally not enough to just detect a prominent frequency of a mode. How much of the plate mass participates in the mode and the relationship to other modes are important things to consider. I've never seen a systematic investigation of modal participation in regards to violin modes, but it is something that is considered essential in the vibration engineering of other structures. - damping: This is the most critical property of any vibrating structure that is responding to a spectrum of frequencies, yet seems to be given the most cursory discussion in design approaches of the violin. I suspect that a good part of the interest in the heat treatment of wood is that it accelerates the natural reduction of damping that occurs in wood over many years across a wide spectrum of modal frequencies.
  7. ctanzio

    The Universe Within

    Interesting video. Thanks David. Putting aside the author's creative use (abuse?) of poetic license to turn varnish into a transcendental experience, I found the detailed microscopic observations to be a peek back in time towards artistic practices, especially when viewed through a lens of modern scientific knowledge. Can we see all the way back to Stradivari? >shrug< An initial observation is that both the wood and varnish surfaces are contoured, i.e., not meticulously smoothed as seems to be a common modern practice. So things like light quality, intensity and angle will have a profound effect on the photos and can be "manipulated" to provide a complex visual experience that may not represent what one may see with a casual observation from a distance. Not really a criticism of the video but rather a warning about reaching conclusions based on how magnified images may look. I've experimented with "rough" finishes and I am not sure if I like it better than smooth finishes. I suspect a rough approach is a way to give more interest to wood that has modest grain detail, while not optimally presenting complex grain structures. I would like to hear other's experience with this. He spends a lot of time observing microscopic accumulations of color, particularly Orpiment crystals. This was a common "yellowish" colorant used 200+ years ago and stretching back to ancient times. It has several interesting physical properties which, IMO, accounts for the variety of colors that can be observed microscopically. Orpiment is poisonous and has been replaced, as a yellow colorant, with a variety of safer modern chemicals. So experiment with it with much caution. In pure form it is a transparent crystal and so allows light to pass through and reflect off the wood surface. Unlike pigments, it is theoretically less likely to obscure grain detail. However, it has rather large refractive indexes depending on the path the light takes through the crystal: 2.4+. Like a diamond, it will tend to "capture" bands of light that will eventually be reflected towards the viewer as brilliant saturated color. If the surrounding varnish does not have similar RI (definitely the case here), then the crystals will be seen as spots of intense color which obscure the underlying grain. This appears to be the case with images at a variety of magnifications. Orpiment also exhibits a property where different bands of light are absorbed and reflected at different angles of the crystal. So it can reflect a variety of tinted yellows that can appear reddish and green, also seen rather distinctly in the images of the video. Cinnabar, also mentioned in the video, has an even higher RI, and can easily account for the orange opaqueness when the violin surface is viewed at certain angles. It is also dangerous to handle. My takeaway is that the varnish is the centerpiece of this instrument with wood playing second fiddle, so-to-speak, to the visual experience. If one imagines the weave of a canvas, it is possible to place paint so that the weave patterns remain visible and add interest to the picture, but the details of the fibers no longer show through.
  8. ctanzio

    Perfection Pegs

    I've had no problem installing the pegs and dressing the ends to look just like wood pegs. The Knilling peg heads are not very elaborate but look no different than common but well made wooden pegs IMO. Because they screw in and cannot be easily removed, one must take extra time to measure, cut and round the ends to get them to look good. With wooden pegs, one can quickly insert and remove the pegs to adjust the look of the ends. Well adjusted wooden pegs can tune as smoothly as the geared pegs from my experience, but the geared pegs never need maintenance and with some practice one dispense with fine tuners on all strings. I believe one manufacturer of geared pegs allows the installation of custom wooden peg heads. Does anyone recall the name of the manufacturer?
  9. ctanzio

    Speeding up suntanning

    UV radiation breaks down chemical bonds in the surface of the wood and creates free radicals (compounds with a net charge that are very reactive). These can then react with other chemicals to create chromophore compounds (chemicals that can absorb photons and then release them in the visible light range). Water is well known to accelerate these reactions. In some woods, these chemical reactions can continue and cause the chromophore compounds to eventually degrade, thus giving a bleaching effect. I am not sure how relevant this is for spruce and maple commonly used in violins, but as you experiment realize that more (UV exposure or water) might not necessarily be better. Also, UV radiation does not penetrate very deeply into wood, so the creation of the chromophores is more a surface phenomenon.
  10. ctanzio

    Working with pigments

    There are two effects here. On the difference in RI and effect on transparency, I think it comes down to what one might consider visually acceptable. For example, using pure linseed oil, RI~1.46, over gypsum, RI~1.56, seems to dull certain very fine features in wood with complex surface structure. But a casual visual comparison between that and a shellac coat might not detect a difference. So the answer here is to make a test sample. If you are using lots of color in your varnish, it is probably a non-issue. But of you are going for a lighter color, like a golden or reddish blonde, I think it can make a noticeable visual difference in the grain detail. The visual effect of light saturation of the varnish and wood surface, a glow so-to-speak, is more related to the RI of the top varnish layer. In general, you want the highest RI and most transparent varnish you can get to achieve this effect. This causes a larger percentage of light to be reflected back to the underlying varnish layers and wood surface before exiting the top layer. There are art conservatory varnishes known for high RI (I don't recall the values now.) But the do not wear well with handling and so are only used on furniture and art that will only be viewed.
  11. ctanzio

    Speeding up suntanning

    IR/Heat treatment is a bit different than UV exposure and so can result in different coloring effects and mechanical changes. Basically, the various compounds in the wood are in a set of slow transitions from one set of compounds into another. The general term for these transitions is "thermal aging". When you heat the wood, it accelerates these transitions. Like UV exposure, the rate of the change is proportional to the density of the initial set of compounds. So thermal aging proceeds rapidly at first, then gradually slows down to a crawl as more of the initial compounds transition to the new set of compounds. The availability of moisture in the air is an important component of many of these transitions during the natural aging process. So if one is trying to accelerate the aging by increasing the temperature, some control of moisture content is needed to reproduce the effects of natural aging. There is a limit to how high the temperature can be before new chemical processes are triggered that would not normally occur during natural aging. For wood, it seems to be as one approaches the boiling point of water (100C). This is not a comment on whether these changes are good or bad for violin making. I just want to point out that you would be entering a realm beyond accelerated natural aging. So many variables to juggle.
  12. ctanzio

    Working with pigments

    The science of turning a cloudy ground into a transparent layer goes like this: The ground must be a chemical that is fundamentally transparent when in a smooth, crystalline form. When in powder form, it may appear cloudy because the facets of the small grains are oriented in many random directions that bend the light into unfocused directions. But if you used a microscope to view the individual grains, you would see that they are transparent. The varnish applied over the ground must have an index of refraction close to the index of the ground material itself. This effectively stops the light from being bent in random directions and causes the cloudy ground to turn transparent. For example, some famous makers on this forum have posted that they use calcium sulfate (gypsum) or calcium hydroxide (slaked lime) as a mineral ground. Both of these minerals are clear, colorless crystals with a refractive index of about 1.56. Various application methods leave the wood looking like it is covered in a dense white powder. Applying a thin layer of shellac, with is refractive index of about 1.53, or some linseed oil varnishes with resin content, also with refractive indexes of 1.5ish, make the cloudy ground turn transparent and the underlying detail of the wood grain appear. I have used the gypsum/shellac methods and it works very well with gypsum of high purity. Any colored mineral that is essentially transparent in crystalline form can also be used as a ground if one covers the ground layer with a smooth varnish layer with similar refractive index. The term pigment is typically used for a mineral color that is opaque. The science of getting a "transparent" varnish from opaque particles is rather complex but I think it has been covered in previous posts.
  13. ctanzio

    Very basic intro to varnishing needed

    This is a complicated topic with many different approaches that yield successful results. I will give you some simple approaches that will give decent results, but for spectacular finishes you will need to study this topic in more depth. Spirit Varnish: Buy a good quality orange shellac and dilute it 50% shellac to 50% ethanol. This will give you a decent work time and allow you to apply it in very thin coats. It will dry to the touch within minutes. You can apply multiple coats without sanding. When thoroughly dry these finishes can be easily sanded, or polished to a very high gloss finish. Spar Varnish: Modern spar varnishes have a longer work time than spirit varnishes and so are easier to apply. High quality spar varnishes are very transparent and give a tough but flexible finish. Polishing the finish can be a challenge but when properly applied it dries to a smooth glossy surface. Oil Varishes: These contain linseed oil as the basic component and various amounts of resins. These are rather easy to apply but take a long time to dry. Special UV light bulbs are recommended to speed the process. These are the most popular finished for professionals but are challenging because of the long dry time. Sealers and grounds are used for bare wood. The main use is to stop the main varnish from soaking into the wood and to allow colored varnish to apply an even color. One or two very thin coats of diluted spirit varnish does the trick. You can use any other type of varnish on top of it. Stripping off old finishes and revarnishing is fraught with problems. The most common is that the stripper can cause some of the old varnish to soak deeply into the wood and give it a streaky appearance that cannot be sanded out.
  14. ctanzio

    Speeding up suntanning

    Keep in mind that there are many different compounds in wood so there is potentially many different types of chemical reactions that can occur that result is color change. I tend to think of wood compounds in two general categories: permanent and extractive. Permanent compounds are things that give the wood its basic structural integrity, like lignin, cellulose and hemicellulose. Casual, short term application of solvents, like alcohol and water, has little affect on these. Extractive compounds are things that are easily removed or added by application of solvents or physical processes like heat and humidity. Resins, oils and water are all examples of extractive compounds found naturally in wood. As a general rule, coloring processes that target permanent compounds tend to cause permanent and uniform coloring, while those targeting extractive compounds tend to cause temporary or inconsistent coloring. UV treatment tends to work strongly on the lignin, a permanent compound. UV + Air = lignin breaks down and eventually forms a stable, yellow compound that is non-extractive. But lignin is also the "glue" that holds the cellulose and hemicellulose structures together. So excessive UV exposure risks compromising the structural integrity of the wood. UV can also cause chemical reactions in the extractive compounds of wood. My current thinking is that "seasoning" the wood, mostly by exposure to reasonable heat for a period of time, causes a good amount of the extractives to evaporate out of the wood. It is difficult to say if this is always a desirable or undesirable thing, but it at least reduces the effect of some variables from the UV tanning process. The rate and intensity of UV tanning is proportional to the intensity of the UV (more lamps and/or higher wattage) and the amount of unoxidized lignin exposed to the UV light. So the tanning process starts out rapidly but quickly tapers off as less un-oxidized lignin is available to the light. To reduce the tanning time, you need to use higher wattage bulbs or more lamps. Make sure the wood remains well ventilated so there is adequate oxygen to complete the chemical process, and do not allow the wood to become overly hot as this risks driving other chemical reactions which can cause unexpected results.
  15. ctanzio

    CAD Which program(s) do you use?

    One can watch promotional videos of 2D and 3D CAD programs and conclude these are powerful AND easy-to-use. Do not underestimate the time it takes to achieve enough proficiency with the program to make it a useful tool. Think about why you want to make a drawing. If it is to experiment with different design concepts for making, say, violin forms, you might be better off revisiting your compass and straight-edge from drafting class. If you are thinking about feeding a CNC machine or performing stress or vibration analysis, then a CAD program that also allows you to automate the construction of finite element grids becomes mandatory. So you want a CAD program that can generate CNC instructions or finite element models.