uguntde

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Everything 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. 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. 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. 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. I hope you are not insulted, but the value is that of firewood. The newspaper inside may be worth more though.
  6. 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.
  7. uguntde

    Viola rib height

    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.
  8. uguntde

    Blanchard Fake?

    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.
  9. 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.
  10. The strong lip at the outside f holes and the edges including the brown varnish look like a bad attempt at some Degani features.
  11. Bernardel made instruments for Northern Africa, which have somewhat ugly pins in all 4 corners.
  12. Very polite way of judging an instrument . Most English concertmasters (orchestra leaders) can't afford anythng like that and still find good souding instruments.
  13. uguntde

    Bow ID

    No stamp on mine - exactly the same nice decortions, and all in nickel. I would say my stick is just Brazilwood.
  14. 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.
  15. uguntde

    Bow ID

    I assume this is a German trade bow, probably not even pernambuco. But the frog, nickel mounted, has some nice chasing. I wonder who could have made this bow?
  16. 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.
  17. That's "Anleitung zur Erlernung des von Hrn. Georg Staufer neu erfundenen Guitare-Violoncells" = Instructons to learn the guitar cello that was invented by Mr Georg Staufer.
  18. Is there any piece beyond Schubert's sonata that was written for the Arpeggione? Apparently the instrument had disappeared by the time Schubert had written it.
  19. 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.
  20. 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.
  21. Thanks for this detailed response.
  22. 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.
  23. Above 1400 it is mainly noise. But I can post it tomorrow. The dynamic range of my setup is limited. I used a Zoom USB mic and switched off all autoscaling etc.
  24. uguntde

    Violin ID

    Guaranteed not Blanchard. Kind of from he opposite side of the spectrum.