uguntde

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Posts posted by uguntde


  1. This is way beyond what a violin maker wants to know, and I just read this varnish chemistry out of interest. From what I read I assume that adding a little phtalic anhydride would make varnish dry faster.

    If someone wants my literature collection on varnishes let me know, I have a lot. There is an interesting master thesis on the internet entitled MODIFICATION OF TUNG OIL FOR BIO-BASED COATING by Narin Thanamongkollit presented to the University of Akron.


  2. On 4/20/2020 at 3:07 AM, Mike_Danielson said:

    I think I need to know more about this.  How much base (calcium hudroxide added?) do you add to the rosin?  The thing that confuses me is that rosin is 100% abietic acid; so it is 100% an organic acid.  The organic acid will react with a base such as calcium hydroxide or sodium hydroxide to make a soap., but I know you cannot react all the organic acid (rosin) and still make a varnish.  The varnish recipe books talk about a 5% addition of base to the rosin--is that what  you mean?.

    I have been studying the literature to find out what is the chemical reaction between linseed oil and rosin when heated, but I cannot find the answer.  It may be the diels-alder reaction that allows them to chemically combine to make a varnish.  Drying of the varnish is by free radicals that crosslink the varnish using the unsaturation--they are naturally present in the cooked varnish and also form by oxygen that penetrates the film plus the action of UV light.  Metal oxides catalyze their formation such as are found in Japan Drier.

    The Mariana manuscript 399 as mentioned by Mrs Merrifield mentions the addition of a small amount of alum to the cooked varnish, and this would supply a small amount of potassium and aluminum to react with the rosin.

    The old varnish makers used a small addition of calcium hydroxide to make the varnish harder and more water resistant.

    regards

    Mike D

    regards

    Mike D

    I am not sure it makes sense to talk about a soap in this matrix as there is no water. Also abietic acid is not a lipid. But reaction with glycerol makes an ester gum which has drying properties. The glycerol will form mixed esters ( groups per glycerole) with the fatty acids of linseed oil and abietic acid. As abietic acis is present in excess it will push the equilibrium towards its ester product. But 2 of the 3 fatty acids from linseed oil can cross link with the fatty acids from linseed oil.

    These reactions are well understood in acqueous solution, as used in Frye's method of making varnish. There you get a soap, and it feeld like soap before adding alumn. In the oily matrix alumn will mainly icorporate some metals. I have also added FeCl2 to get some red colour (you really want FeCl3 but it is oxidised in situ).

    A base is probably simply a catalyst. It makes the process a but faster. Addng metab oxides probably also catalyses the 2nd reaction, the corss linking - the process is a completely different reaction, probably involving radicals.

     

     

    Abietic acid is an organic acid


  3. On 4/17/2020 at 6:14 PM, David Burgess said:

    Does that create the possibility of ending up with a varnish which is excessively alkaline? Or does anything which isn't used up in the neutralization process fall out somehow?

    In acquesous solution esterification (this includes cross-esterification) is base or acid catalyzed - I assume that is the same when you cook varnish in linseed oil. In my opinion what you do when you cook varnish is a cross-esterification. You remove the 3 fatty acids (linoleic acid, alpha-linolenic acid, and oleic acid.) from the glycerole, and you add some abietic acid, i.e. abietic acid replaces fatty acids on the glycerol, probably depending on the ratios. Oleic acid can not participate in the reaction and probably acts as a kind of softener. The base would work as a catalyst, speeding up this process. In some cases I belive I saw a bubbling effect when adding lime later, but this observation may be misleading, as I added it in water which may have caused all the bubbling.

    When the varnish hardens it is mainly the alpha-linoleic acid, but to some degree also the linoleic acid that undergo reactiions via their conjugated double bonds (probably light induced Diels-Alder reactions). This is why linseed oil hardens even without rosin, i.e. without the abietic acid. But you get better cross-linking and a harder varnish with the abietic acid, which also has a conjugated double bond. There are a lot of older patents about this from the varnish industry as they use the same principle. For industrial varnishes the hardening is of course usually not light-induced but radical induced because it is faster. But the process is a different one.

    If this is correct, and I admit it may not be, adding a tiny bit of KOH or carbonate should be even more effectve that adding lime to the cooking process. Lime is an odd choice as it leaves silicates and dirt that is difficult to be removed afterwards.

    I would be interested to hear other opinions about this.


  4. On 3/18/2019 at 2:13 PM, Michael_Molnar said:

    I used to follow Tad Spurgeon's washing method. What a mess. So I switched to Varnish Maker's Linseed oil sold by Woodfinishing Enterprises. It is clean and works like the proverbial charm. 

    I squirt a few grams of lime water paste into the hot oil and hot rosin to reduce acidity that attacks most pigments. I posted photos somewhere doing this.

    I do not use mastic, but someday I just might do it. So far I have seen no need for it, but I like to experiment. Remember that it burns above 100 C. 

    As for the pill, I just shoot for 2 or 3 inches. It's usually one thread. 

    The only time I have seen bubbles pop up while brushing was due to cold turpentine thinner. Slightly warmed varnish helps to eliminate volatiles..  I think dirty brushes can be another source. I clean my brushes thoroughly first with turpentine, then wash religiously with Ivory (pure) soap. Smell the brushes for remnants of varnish. The brushes must also be completely dried before using. Another test for clean brushes is to flick the bristles in bright sunlight to see whether any dust flies away.  I store the brushes in a large closed jar. As my high school chemistry teacher taught: Cleanliness is next to godliness. 

    Be patient and expect setbacks. It's a learning process.

    The lime is still a mystery for me. I think it is the catalyst for alcaline cross-esterification, replacing lipids with abietic acid. Am I wrong?


  5. On 8/7/2015 at 3:18 PM, MANFIO said:

    Antoine Tamestit is playing Harold in Italy here with our State Orchestra so I had the oportunity to meet him for some viola test drive, and see and listen to the "Mahler" Strad viola.

     

    He produces a beautifull sound on it. The instrument is in mint condition with lots of coloured varnish. As mentioned by the Hills the head is not in proportion to the body, being oversized.

    In a 2018 recording on youtube

    he seems to play a modern viola. WIkipedia says he owns a Vatelot. Or is this the Mahler Strad you are talking about?

    Here he shows the Strad and it looks different.

     


  6. A while ago I studied the Guadagnini violas on Cozio. I started with Hargrave's blog on a Guadagnini he found in China. He says he lost his notes at one point, or they were stolen, but still gives a good description of that instrument.

    Several on Cozio had the same body length (402mm, just above 16"). The rib hight was consitently 37/38. I find violas with a powerful C string benefit from tib height up to 39/40. Rib thickness is also important as much of the C-string sound is an air resonance.


  7. A Blanchard is very hard to fake because his workmanship was quite exquisit. If it is a fake it is easy to identify as such. Glue marks could only be from a bad repair. The difference in price tag of a Blanchard and a fake is at least a factor of 10. Whether there were others in Blanchard's workshop who made instruments and used such a label I don't know.


  8. The reaction of rosin and linseed oil is chemically a cross-esterification. Lineolic acid gets attached to abietic acid. In solution such reactions are base catalysed. I assume that something like this is happening in hot rosin, especially, as the lime is added in water. Lime light just catalyse the ester cleavage of the abietic acid. Industrially anothet catalyst is used which I need to look up. This is just an assumption, as I know little about such chemistries.


  9. 9 hours ago, martin swan said:

    We recently sold a Tomaso Eberle to a concertmaster. It was a very archetypical Neapolitan violin - quite screechy close to the ear, not unattractive in sound but definitely "penetrating".

    His main concern was that everyone in the orchestra (particularly the strings) could hear him, and he paid a lot of attention to the articulacy of the instrument in fast passages. We tested this with a few of his colleagues in a hall, and while everyone agreed it wasn't the nicest sounding or most sophisticated instrument I took along, they/we all agreed it was the most audible and the "crispest". 

    I think if he had been a soloist, he would also have wanted a more malleable or beautiful essential tone. 

    Very polite way of judging an instrument :). Most English concertmasters (orchestra leaders) can't afford anythng like that and still find good souding instruments.


  10. On 2/1/2019 at 6:36 PM, martin swan said:

    The value of a violin relates to its degree of separation from a Stradivari (or a DG), nothing else.

    Being made in the same country as a Stradivari gets you higher up the list and makes up for all sorts of other shortcomings - terrible model, poor workmanship, inconsequential sound etc. 

    This profound injustice is the reason why so many great contemporary makers are pissed off most of the time ... 

    For every one of the really good Italian makers post-Stradivari you can find a Prague/English/Dutch/French/South German maker who consistently produces a similar quality of sound for a fraction of the market value. 

    WHat Martin describes has been the case for many centuries, but now modern makers from Italy don't have much of an advantage any more. American violins are now probably the most expensive, driven by soloists who used their instruments (e.g. Stern and Zygmutovicz).

    If one wants a 19th or 20th century violin there are some real beauties from German makers. Gärtner, Winterling are among my favourite 20th century makers. Investment wise it is Italian (Fagnola, Oddone, Bisiach ...).  They were also good, but not better than the best German makers of that time.

    Much of this market is now driven by Asian buyers. Unlikely that German violins will surge in value, maybe except for good authentic Kloz family violins.

    For good German instruments it is a buyer's market.


  11. https://simpk.de/arpeggione_790.html

    They say it is tuned E-A-d-g-h-e' as a guitar (h=b).

    Here a blog about it:

    http://arpeggione2009.blogspot.com/2009/08/arpeggione-stauffers-model.html

    And wikiedia also has the information about the tuning

    https://de.wikipedia.org/wiki/Arpeggione

    according to which the only old piece is that by Schubert but since a copy of an Arpeggione was made some more have been written for it (probably transcriptions).

    This is what it sounds like:

    Intonation isn't great.


  12. There is this article, www.jpschmidtviolins.com/Violin_Acoustics_2.pdf
    which I think is by Don Noon, our fellow maestronetter. It refers to this average table in the Strad for the 'key modes' of Stradivarius violins (I attached a screen shot of the spread sheet). I wonder whether anything along these lines exists for violas. What viola sound are we looking for? I know what I like, they must not be 'nasal', I like a strong C-string, I like it if they also have an edge in the upper strings (whatever this means). I have hardly every seen a viola at an auction that I liked.1836963595_Screenshot2018-12-30at21_47_17.thumb.png.35e3b8d56a508121fe25ef4373e2f302.png


  13. 18 hours ago, Don Noon said:

    That has been one of my pet peeves for a long time, and it's even worse than "signature modes", but just the mode frequencies that seem to get the vast majority of the attention.  I grant that the frequencies matter, but the amplitudes have a huge impact on the tone, and I can't recall any substantial work on how to control that aspect.

    I think it's pointless to try to look at individual modes in the higher ranges, but it is definitely a critical part of tone.  You don't have to work with names, but consider them to be sheep that might be herded in certain directions.

    I am trying to get the higher frequencies - they depend a lot on the environment, one almost needs a sound isolated room - which I do not have. Any laptop fan in the background will add a signature. Higher frequencies from from frequency modulating power supplies (dimmable LEDs etc) all add to that sound spectrum. 

    I work a lot with frequency analysis in science (I do something called NMR) and we would not accept a signal that does not have a signal to noise ratio of around 5 and is clearly reproducible.


  14. 11 hours ago, Don Noon said:

    For the first one, it is fairly clear to me:  231= A0,  321=CBR,  374/385=B1-, and 453=B1+.  Although we commonly just talk about these modes as if they are the only things there, quite often there are bumps and blips around them that can muddy the picture.  I wouldn't worry about trying to identify all the other higher peaks, as they vary a lot from instrument to instrument.

    For the second one, 210=A0, and 342=B1-, or perhaps a combination of B1- and the CBR.  The B1+ is surprisingly weak, but I"m sure it's there in the 400 - 440 range.

    FWIW, this is my VSA tone award winning viola (40 cm), analyzed with impact and bowed semitone scale.  The A0 and B modes are rather obvious, although I expect the bowed result shows a combination of B1- and CBR.  In my  experience, the CBR shows up much more strongly under bowing than it does for impact.  The bowed scale is also shown at lower resolution, to avoid the granularity of the single notes.

    11032440_Viola29.jpg.a1f76082b8376c80e523dfb841c4586b.jpg

     

    I agree with other posters that above 1400 Hz is definitely not "noise", although it is so chaotic you'd be tempted to ignore it.  Trying to analyze it to determine what it sounds like, or if it's good or bad, is a pretty impossible task... but the same thing can be said about any part of the response spectrum. 

    About the only thing you might be able to tell from the first two instruments is that the second one has lower resonances, and more power down low, so is likely to have a deeper sound.  You could probably say the same thing by just looking at the size difference.  Good or bad is far more difficult to determine, likely involves a lot of what is going on at the higher frequencies, and in the end is personal anyway.  About the only thing I can say is that huge gaps in the response are probably not a good thing, as well as excessively high peaks.  But then, trying to figure out what to DO about it is another impossible task.

     

    Thanks for this detailed response.


  15. Usually for violins only frequencies below 600Hz seem to be considered for A0, B0, B1, B1+

    http://www.catgutacoustical.org/research/articles/modetune/modechrt.html

    Schleske looks into the noise at higher frequencies but then one needs a more dampening window function. He also reads a lot out of some noise:

    http://www.schleske.de/en/research/introduction-violin-acoustics/sound-analysis.html

    One should average these signals, this is what we do in my field, NMR spectroscopy. We ust average equal signals until S/N is stronger. The type of frequency analysis is similar (except that you can't get a complex signal, i.e. two orthogonal signals, from a violin).

    Schleske also plots the x-axis chromatically, which I assume means log2 scale, as any double frequency is an octave. Audacity can't do this, but I can use matlab if I can figure out how to fft a signal that is not complex (i.e. of two rectangular channels). Maybe a HIlbert transform and then a power calculation?

    All this has been figured out before but is not well dcumented anywhere. At least I can't find it.

    My fundamental question is which resonances should be strongest for a good sounding viola.