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Author Topic: Violin finishes  (Read 18383 times)

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Offline giannaviolins

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Violin finishes
« on: Dec 18, 2008, 12:45:07 PM »
Originally on fiddle hangout.  Might prove amusing for some.

We've had some discussion of finishes lately. They're very interesting. Gianna and I started out doing spirit finishes we made, then commercial oil, then making varnish. I've listened and read what I can get ahold of. Some varnishes published simply don't work. It's not me - eventually I'll find someone really knowledgeable who indicates they don't work and never have! But they're published.

Manfio's varnish and finishing system he presented was extremely interesting to me.  (see fiddlehangout) It's pretty much where I ended up after doing this and that, up to and including wiping down some finishing jobs I didn't like.

The pieces I'd picked up from here and there all came together much better through my encounter with two bodies of information. First, I spent a little time with and heard a lecture by Nagyvary. Played one of his fiddles. He's quite a character, and there's lots of spin and interpretation. But his factual observations are quite interesting. Note I'm not buying into his whole construct. But he's clearly worked at gathering data as well as developing marketing.

http://www.springerlink.com/content/jhq2u661m7867611/ provides a particularly interesting look. Can read the first page. And http://www.sciam.com/article.cfm?id=secrets-of-the-stradivari provides some pop-oriented context. While this is later, much of it was presented when I saw him. Probably 2000.

The other cool piece of information was Padding's article in 2005. See http://www.classicalvarnish.com/VSA%20Papers%20Padding%2011-25.pdf I read that when I was about to go to DC. Proceeded to look at old paintings and coatings at the museums. Everything i saw matched the article and made the process of generating this stuff look much more reasonable. Even makes painting my house seem more rational - get down to the wood, use a penetrating fungicide and wood prep to prime, seal with an open coat paint designed to stabilize the surface and give grip to the top coats, then apply high-solid content paint. So we still do this stuff, we just don't think about it that way.

The articles are worth reading. And will explain why I have complicated considerations when folks discuss varnish.

I was also likely pre-conditioned for complex finishes from doing fancy lacquer on bicycles. Have to prep the metal, put on a primer binding into the pores (sealer), build that up to nicely level (ground), then a color (usually a reflective metallic) and follow with tinted coats (dyed I think, rather than pigmented), and top with clear. Spending a fair number of hours rubbing out. I think I'd do powder coat these days!

Padding studied medieval painting methods. Planks covered with 2 layers of hide glue, first to sink in and prime the surface, second to further fill the surface and keep the overlying material from sinking in. Third was glue with minerals to fill the surface. Then the colored layers, then clear oil varnish.

Padding's description makes sense to me. He extends this to a model for classical coatings on violins, which in conjunction with other's work is quite compelling.

1. Priming to both prepare the substrate and influence its properties. Could be just smoothed or could even be treated. And other treatments could have influenced wood prior to turning into a violin. Like we do with pressure treating. Not that pressure treated wood should go into violins. Treatments could harden, color, and protect the wood. Nagyvary postulates borax treatment, still used today. Others write of ponding with bacterial attack changing the wood. I've also read of strong chemical salts postulated as almost melting the wood. I don't have a personal opinion. Borax does something, but I don't know it's long term effects. Safe enough on spruce strips!

2. Sealing to prevent the ground from sinking in. Padding points out that too much sealer is bad. This jives with my experience in testing plant gums. Two coats and the surface gets weird, the ground doesn't want to stay on. Nagyvary in his lecture ca 2000 indicated plant gums were used to seal, and he presented the same hypothesis or observation in the interview I cite above. This jives with the vernice bianca, gum arabic, and similar sealers found in the literature. Makes the wood pretty, too.

3. Ground. Particulates. Nagyvary, Rubio, Woodhouse, Padding. Everyone points to the importance of the ground and its special properties, and points to the mineral content. But usually it's in general terms. The 1988 Nagyvary paper highlights what might be crucial differences. Ca 2000 he showed even better photomicrographs and a wonderful cross section showing layers of ground and varnish. The particulates in the ground range from extremely tiny to just small. Maybe this mix has something to do with the properties of the ground.

4. Painting with highly pigmented varnishes. Nagyvary's nice images showed layers of different colors, the color provided by finely divided minerals, densely packed. We tend to paint violins. Pigment in a transparent medium.

5. Varnishing to even up the reflection and protect the paint.

Whether all these steps are on every classical instrument is pretty debatable. But maybe.



1. So. The wood might have been treated. We have nifty ways of treating it today. Maybe someone is duplicating it, knowingly or not. We not only have ponding, baking, boiling, borax as in the old days, but cryogenic tempering, modern chemicals (minwax wood hardener - please do not use this!!), and who knows what else. Room for experimentation. Some minerals would possibly get in by rubbing out with pumice or other minerals. Something that gives good optical qualities is going on, anyway.

2. Sealer. Usually this seems to get done one way or another. Shellac, burnishing, organic gums, stiff oil varnish in conjunction with the filler.

3. Ground - that Barlow and Woodhouse particulate ground, minerals in drying oil. Something I don't see much attention given to the extremely fine particulates. These are much finer than we usually use for anything, and are of mixed sizes up to those visible in optical microscropes. See the 1988 article. This may be very important if the ground serves a key acoustic role.

4. Paint. Strong color, thin, applied very evenly. I'm not adverse to Padding's hypothesis that sponge or hand application was common. It makes for an ugly finish with modern coarse paints, but the pigments may have been very fine for the classical paint layers. Also, if the varnish used thinned greatly as it dried (as Manfio's does), then pigment initially distributed through a thicker layer settles down on the wood as a thin, intense layer. I've seen this with my mastic varnish, which is similar to Manfio's. Thanks to Van Dusen and Darnton for that varnish!

5. Varnish. With thin paint, we don't even need this. Although I know at least one modern maker who routinely does light French polishing to even out the sheen on his violins.


Something not discussed much is a reason the classical ground provides acoustic advantages. Work with conformal coatings on speaker cones might provide some insight. When the coating has a speed of sound much higher than in air, the speaker more accurately reproduces sound. Looking at a "fast" ground on a violin, the ground would quickly wrap the violin in energy. But the complex nature of the ground and the inherently lower speed in the wood could continue to excite the instrument. I can draw up guesses about what's going on, but that's all they'd be, are guesses. But something is going on in the old fiddles, and maybe this is part of it.

Just testing the grounds would be helpful. Measure speed and perceived tone quality from wood strips treated with different grounds, and with the same ground made with different minerals. A problem is getting the very fine particulates. I'm not really sure where to get them! Certainly the "Rubio" ground materials look way too coarse. Or maybe they just need fines added.

Nagyvary (I hate to keep bringing him up, but his data are interesting) calls the combination of varnish and mineral a "nanocomposite." I think he's right to do this, and right to point to it as a possibility for the classical violin's superior tone. Nanocomposites are used in all kinds of things. I've yet to find a nanocomposite varnish, though! Maybe I'm not looking in the right place.

Just my observations on a couple of interesting publications and a talk. There's lots more information out there well worth perusing. I'll have a fiddle to varnish soon and all this work that's been done gives me lots to think about. I probably have to make up the varnish anyway, which will take a week or two.

Maybe I'll do a dense pack diamond ground.  Wouldn't that be cool?




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Offline Don Stackhouse

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Re: Violin finishes
« Reply #1 on: Dec 18, 2008, 04:36:41 PM »
For extremely fine particulates, what about fumed silica? It's used as a thickener in epoxies and gel coats for fiber composites, and is fine enough to be considered a respiratory hazard, capable of causing silicosis (in other words, fine enough to fit into the alveoli in your lungs, which is quite a bit finer than most "everyday" particulates).

Common brand names are "Cabosil" and "Aerosil". Quite a number of sources, such as Fibre Glast Developments, Composite Structures Technology ("CST") and Aircraft Spruce and Specialty.

Offline giannaviolins

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Re: Violin finishes
« Reply #2 on: Dec 18, 2008, 04:59:07 PM »
Excellent!  Probably less expensive than diamond powder.

Offline cnaill

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Re: Violin finishes
« Reply #3 on: Dec 19, 2008, 01:10:46 AM »
If your finish ideas turn out to look like the Messiah, you do well. I agree it is amusing, but is a different way.  :laugh:

http://www.burgessviolins.com/Messiah2.jpg

chuck

Offline giannaviolins

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Re: Violin finishes
« Reply #4 on: Dec 19, 2008, 02:09:56 AM »
What do you mean, amusing in a different way?

The Messiah is highly illustrative of the old finishes of Stradivari.  Most have been polished off over the years, rather than preserving tool marks.  The Messiah illustrates how the finish settled down over the woodwork, and shows the dense coloring of the varnish.


Offline ChrisP

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Re: Violin finishes
« Reply #5 on: Dec 19, 2008, 11:10:37 AM »
Don, would fumed silica have been available in Strad's day?

Offline giannaviolins

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Re: Violin finishes
« Reply #6 on: Dec 19, 2008, 12:14:27 PM »
I can't find much information on historic grinding techniques.  The materials are well known from analyses of minerals found on violins - see rubioviolins.com re the Woodhouse & Barlow paper.  And from historic information on paints, for the coloring information.

The most interesting aspect to me is the very fine grinding.  I haven't been able to find independent or written information on grinding, but I heard in a lecture that hand grinding over long periods will give a wide range of particle sizes.  Down to extremely fine.  Then a water sluicing technique would separate out the fines, including the very fines.  That accounts for the wide range of sizes down to exceptionally tiny.

The material in the ground is a mix of minerals.  Silica is a mineral.  All have pretty fast speeds of sound.  So a mix of silica particles likely has a similar effect.  The size and general composition is likely pretty close.  So far I've been unable to find the size distribution in the silica fillers. 

Something Rubio did in his evolution of a ground was to cement the minerals to the surface with potassium silicate.  The Padding article instead postulates oil varnish as the carrier for mineral particles.  This would make a tremendous difference.  As might the saturation with rosin oil used by Rubio.  I have tested both approaches and decided to not use potassium silicate.  Although I can no longer remember why.  I probably have my notes somewhere.  I still have potassium silicate, so I can do some strips if I want.  But I think I'd rather go with the Padding approach.  That statues and other materials may have been treated with a cementing material doesn't mean that violins necessarily were.

Offline woodwiz

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Re: Violin finishes
« Reply #7 on: Dec 19, 2008, 03:09:10 PM »
I think you rejected potassium silicate because it sounds bad.  At lest it has for us.

As to fineness of particles, I understand that the way ground minerals like pumice were sorted was to mix thew with water to get a suspension, let the coarser solids settle, and then pour off the remaining liquid (supernatant)  by doing this floating and settling an umber of times one could get down to particles fine enough that they would remain in suspension for a long time.  Can't say what that would be in microns, but it's pretty fine.

The grades of pumice abrasive, F through FFFF, are related to the number of "floats" the particles made it through.  The same could have been done with the pozzolana ash available around Italy, which, IIRC, was the major ingredient in Roman hydraulic cement.

Offline Don Stackhouse

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Re: Violin finishes
« Reply #8 on: Dec 19, 2008, 05:05:05 PM »
As far as particle sizes of fumed silica, I found a fair amount of info on Cabot Corporation's "Cab-O-Sil" here:
http://www.cabot-corp.com/cws/businesses.nsf/CWSID/cwsBUS01182001091331AM6866?OpenDocument

Apparently the particles are like irregular skeins of yarn, extremely porous, with enormous surface area. The average particle diameter appears to be around a tenth of a micron (100 nanometers). That's pretty small!

As far as whether it would be available in Strad's time, no, the processes used to make it did not exist then. However, as others have noted here, there were methods available then for generating and/or sorting powders of silica and other materials that were extremely fine, possibly as fine as fumed silica. For that matter, it's not inconceivable that the finest pumices generated in volcanic erruptions might create something similar in structure and fineness, which could then be sorted by water flotation methods. We do know that pumice of various forms was used extensively in grounds.

However, the whole question of whether Stradivarius had access to fumed silica (and the implication that it therefore might not be "legit" to experiment with it in violin varnishes) does remind me of an old joke:

Q: "How many luthiers does it take to change a lightbulb?"
A: "Twelve; one to hold the ladder, one to screw in the new bulb, and ten others to argue about how Stradivari would have done it."

Fine tuners, metal core and synthetic strings, nylon tail guts with adjustable brass retainers, modern length and configuration necks, and a number of other things commonplace today did not exist then. I would hope that in the past three centuries of development and experience we have learned something beyond just the mindless parroting of the work of a few 17th and early 18th century artisans in Cremona. Not to disparage Antonio and his contemporaries by any means, but if I were to contribute something to human history and culture that had the sort of lasting influence that their work did, I would be profoundly disappointed if no one bothered to expand on my work after that.
« Last Edit: Dec 19, 2008, 05:18:39 PM by Don Stackhouse »

Offline giannaviolins

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Re: Violin finishes
« Reply #9 on: Dec 19, 2008, 06:04:18 PM »
Pot. sil sounds horrible to me.  I didn't like the effect on test strips, so I never used it.

The modern silica doesn't seem like the fine crystalline materials in varnish and ground.  Maybe I'd be better off with fine diamond! 

Offline sreizes

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Re: Violin finishes
« Reply #10 on: Dec 19, 2008, 06:25:56 PM »
Well, speaking from ignorance of lutherie, what about volcanic ash and clay as a souce for fines?  Both contain complex alumino-silicates down to ultra fine coarseness, clay by definition is an ultra-fine material.

Offline giannaviolins

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Re: Violin finishes
« Reply #11 on: Dec 19, 2008, 06:37:14 PM »
See mineral ground http://rubioviolins.com/

Offline sreizes

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Re: Violin finishes
« Reply #12 on: Dec 19, 2008, 07:53:32 PM »
Hmm, not sure I followed you there Steve.  In the article you refernced, he seems to have used the pure componds (chemistry style) as opposed to the raw earth materials.  Is the supposition that the matierals for ground were being aquired from an Alchemist (chemist/supplier) of the time or that they were prepared by the artisian?

BTW, that chemical analysis looks a lot like a nice blend for feldspars to me...

Offline giannaviolins

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Re: Violin finishes
« Reply #13 on: Dec 19, 2008, 08:15:50 PM »
I didn't write anything to follow.  I just pointed to the rubio page, which is interesting.  Look to Barlow & Woodhouse analysis.  Then you've got one interpretation of how to do that.  There's also the Padding VSA article with another approach.


I have some of that rubio material from Kremer, given to me.  I have used it.  It is very fine.  Mixed with the silicate, it appears to be perfect for coating things that aren't supposed to vibrate.  Mixed with good strong oil varnish it makes for a nice ping.  It might be too uniform. 

I'd like to do a violin with the rubio earth mixed with very fine diamond powder, and with the overlying softer varnishes colored with very fine mesh glass powder.  That would be fun.

Offline Don Stackhouse

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Re: Violin finishes
« Reply #14 on: Dec 20, 2008, 04:52:27 AM »
I suspect you might also need to look at both the shape of the particles and the chemistry between them and whatever binder you use. From a structural standpoint, if you don't have a very strong bond coupling the particles to the matrix,then you will end up withwhat amounts to tiny marbles rattling around in pockets in the matrix. That's going to act a lot like the contents of a "dead blow" hammer, brutally obliterating any vibrational energy that comes anywhere near it. That's where you might be a lot better off with the fumed silica, it's going to bond securely to the matrix. I doubt that diamond is going to stay attached to the varnish matrix, especially after it's gone through a few temperature cycles.

Offline giannaviolins

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Re: Violin finishes
« Reply #15 on: Dec 20, 2008, 05:17:00 AM »
Good point.  So what is the solution?  The grounds appear to be some matrix full of all kinds of particles of very fine to fine.

Offline Don Stackhouse

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Re: Violin finishes
« Reply #16 on: Dec 20, 2008, 02:03:34 PM »
First of all, I don't think the porous nature of the fumed silica will necessarily hurt its performance as a filler. It may actualy help it. It certainly does for its structural properties in advanced composite structures. Also, we haven't seen what the actual nature of the particles in very fine volcanic pumice is (anybody know of a link with SEM photos of the stuff?). It might be surprisingly similar.

In any case, I think we're getting back to something I learned about engineering a very long time ago. Almost without exception, the problems discussed in the initial analyses turn out to be phantoms, and the real show-stoppers turn out to be the problems that no one anticipated. It's important to get some "breadboard" or "proof of concept" tests running as early in the program as possible, so you can sort out the real problems from the imaginary ones.

With that in mind, I have some spruce test strips I just got from Simeon Chambers, and I also have about ten cubic feet of thixotropic silica over at our other shop, and a fairly fresh bottle of Vernice Bianca in the fridge. I also have a little bottle of alum, and I could probably find some clay down by the creek. Steve, I could make up a test sample or two, or I could send you a sample of fumed silica for you to play with (of course I'd want to make sure you were expecting it, these days sending a package of fine white powder to someone through the mail is a good way to get arrested!). I don't have any diamond powder, although I do have some carbon powder. Anyone have a source for finely ground quartz? What about ground amber?

If I'm making the samples here, I could try other matrix materials (oil or spirit varnishes, etc.) that anyone cares to contribute.

Offline Don Stackhouse

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Re: Violin finishes
« Reply #17 on: Dec 20, 2008, 02:38:41 PM »
The other possibility that crossed my mind was mechanically milling the fumed silica, so that the fine, stringy, porous particles get broken up into even finer but more nodular particles. I can think of a couple ways to do it. The particles are already crystalline, but elaborately branched, like the ice crystals in frost. breaking them up into smaller bits shouldn't bee too difficult. It might be possible to infer the "degree of nodularity" simply by measuring changes in the angle of repose; more nodular particles will have less tendency to interlock, so will flow at a shallower angle.

Offline giannaviolins

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Re: Violin finishes
« Reply #18 on: Dec 20, 2008, 02:57:58 PM »
Matrix either needs to be something available in the 18th C or something stable and better.  I'm thinking some of the artist mediums dense packed with nano to micro particles that remain transparent would be about right, but that's just a guess.  The liquid silicate treatments lead to coarse sounding instruments that eventually break in and are OK orchestral violins for filling in, but are never really pleasing.  And that's on the good side - some remain brittle and harsh, hard to get going.  

What I'm looking for is a fast material, high speed of sound.  That's why porous things didn't seem to be ideal.  

If I get a chance, I'll . . . .  well, that's not going to happen today.  Busy.  Leaving Monday.  

Fairly dense packed mixed material down to nano sizes in a matrix or glue, resistant to wear, that's what seems to be established.  Given that the speed of sound through minerals is higher, I postulate that an increased speed of sound in a well-bound conformal coating increases the speed and excitation efficiency of instruments, as it does in other transducers, providing a cleaner, less distorted sound.  Conformal coatings along with other features designed to reduce distortion are proven in other fields.  So the presence of a resistant conformal coating in the better old violins interests me.  But too hard and mineralized (potassium silicate and the like) don't give the tonal results that consistently please.

While it's just part of the equation, a fast ground might be a good part of it.  

From an efficiency and production point of view, having yet another material around seems troublesome.  

Fine grind mixed minerals, water settle briefly to get the chunks out, then decant and dry.  There's a fine filler generated using techniques available at the time.  While I can't walk into Woodworkers Supply of Cremona{WSC), I strongly suspect a range of fillers including ground rock fillers were available.  They came from somewhere.  

Why this stuff?  Maybe chalk and gypsum don't go transparent very easily.  Or don't give as much resistance to wear, if that was a criterion.  Regardless, the mineral mix appears to have been used.  

So the binder.  For paintings (and a violin is painted), the gesso binder would be animal glue.  Tends to crack in thick layers, and there are thick layers on some violins.  

OK.  I grab some fillers from WSC.  Gypsum, powdered chalk, powdered minerals.  I try rabbit glue.  Soaks in when thin, has to be hot, a pain to mix up.  May sound funny.  The gypsum and chalk leave a white haze, look bad.  The minerals look better, more transparent mostly.  Maybe.  Reach for another binder.  What's around?  Oil varnish, probably from down at WSC.  Sets slowly, let's me mix the materials in to form a slurry.  Smear or roll this on some wood.  It that a resistant layer?  Maybe.  That's what Padding postulates.  

I did a bunch of these tests a long time ago.  I can't recall the results clearly, except I ended up for quite a while using vernice bianca sealer overlain by oil varnish with rottenstone & tripoli as a filler.  But a lightly mineraled filler.  Can hear the difference and it was an improvement.  I'm thinking I might have not nearly loaded up the filler layer sufficiently.  Not that it needs a thick layer, but a densely loaded ground layer might be the ticket.

But I don't know.  I'd like to have a proven perfect finishing system that produces great results.  I liked the KC violins woodwiz brought.  They sounded very good.  So their ground is working.  

Anyway, I have a bunch of mineral type things at work.  I might try some test strips.

Any experiments would be great.  

Wood treatment to get speed of sound in top wood more equal between along and transverse.

Conformal coating, high speed of sound, to wrap the instrument in vibration right away with every input.

Resistant coat to match the better old violins.


Offline Don Stackhouse

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Re: Violin finishes
« Reply #19 on: Dec 20, 2008, 04:26:10 PM »
...What I'm looking for is a fast material, high speed of sound.  That's why porous things didn't seem to be ideal. ...

If the porosity in the particles (actually they are not so much porous as dendritic) was full of air, that would be true. I'm thinking more along the lines of a fiber composite. If the particles are completely saturated with the matrix, no air bubbles, then the fact that they are porous is no longer relevant. In fact, the long, dendritic structure of them may actually provide a better pathway for the sound, acting like channels through the matrix, like the glass fibers in fiberglass.

I have some walnut oil varnish (which is quite thin, so it should permeate the particles well) and some Vernice Bianca. I'll try some test strips. How are you testing these?

Offline giannaviolins

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Re: Violin finishes
« Reply #20 on: Dec 20, 2008, 04:37:10 PM »
Tap.  I'd like a Luchi meter.

Offline woodwiz

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Re: Violin finishes
« Reply #21 on: Dec 20, 2008, 05:10:58 PM »
Actually, in our experience, a good ground changes the voice of a violin from "eeeeeeeeee" to "aaaaaaaaaaaaaah".  Suppresses some annoying highs, and brings out some other, more desirable frequencies. 

Two fundamental questions: 

Does increasing sound transmission speed produce the desired result?

Which grounds speed up sound transmission, and by how much?

Anton learned everything he knows about grounds from trial and observation of incremental changes over a lot of years, so I haven't got a clue as to the answers to those questions.  I'd definitely be interested in any data from controlled experiments.

Anton's ground is a mineral ground, but that's about all I can say about it.  It's his only secret.


Offline giannaviolins

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Re: Violin finishes
« Reply #22 on: Dec 20, 2008, 06:20:21 PM »
In other transducers, a conformal coating with a sound transmission speed greater than that of the substrate greatly - I am not exaggerating - GREATLY increases clarity in a way that sounds to me like the reduction of intermodulation distortion.  A reasonable model someone can test for this is that the boundary layer of air over the surface gets excited all at once, rather than over a longer period of time.

I'm wondering if part of the effect is like that of getting the water "live" in a tow tank prior to running a model down it.  Combing the water ahead of the min-vessel to get smooth and accurate waves. 

Intermodulation distortion shows up for me in a harshness in the top end, where the excess and bad harmonics mix.  Reducing this distortion results in a quiet background sound and a clean, clear, open primary sound.  Noise level drops very quickly. 

Most of my testing has been on guitars and is rather interesting. 

My limited testing on violins with intermodulation distortion reduction focused primarily on the bridge and F holes.  I haven't done a conformal coating intentionally designed to modify the transmission of transverse waves along the surface of the material, but it's been done in analogous fields with stunning results. 

I'm thinking that part of the effect of putting a comformable coating on the wood surface, strongly bonded to it, would be to impact the sound transmission characteristics of the whole surface.  Sheet of foam vs. foam core.  If that conformable coating is fast, then it could be a good thing.  Given the high concentration of particulates of mineral origin reported in the magic ground, I would expect it to have a relatively high speed compared to straight varnish. 

And I'm hypothesizing that high speed is good.

But not if it results in a surface that transmits excess gritty high-end noise.

The result achieved by the ancients may well be obtained through a combination of treated wood, great design and construction, and the specific primer/sealer/mix common to the period, followed by that ground.  It's also possible that just the right ground without the right sealer or primer or treatment gives highly inferior results.  A complicated thing.

Offline Don Stackhouse

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Re: Violin finishes
« Reply #23 on: Dec 20, 2008, 06:42:14 PM »
I wonder if this is analogous to those copper-bottomed pots and pans, where the copper conducts heat laterally along the surface much faster than it can conduct through the thickness to the inside surface of the pan. This wicks heat away from any hot spots and into any cold spots, evening out the temperature distribution over the surface.

Conceivably a "fast" ground could have a similar effect, spreading out the acoustic energy in "hot" spots and delivering it to the "colder" places, resulting in a more organized and uniform motion of the plate, a clearer sound and more efficient sound production.

Offline giannaviolins

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Re: Violin finishes
« Reply #24 on: Dec 20, 2008, 07:45:12 PM »
Those are exactly the concepts presented in working with conformal high speed coatings elsewhere.

 




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