uguntde

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Everything posted by uguntde

  1. With violas we see a new taste in instruments that are more than just orchestra background noise. The viola suffers from an unfortunate geometry. Unlike the cello the body is too small and the fingerboard too short. If you play on the higher A string it sounds forced, and on the C it is often nasal. It is unlikely that the viola will ever reach the grandeur of the cello, it just has unfortunate dimensions.. Many makers tried to improve the viola. If you go to the instrument museum in Brussels you can see lots of Vuillaume's attempts of a mix between viola and cello. None of them survived. Nowadays modern makers have improved the viola a lot. This started with Tertis who had himself made violas with an increased air space by using 17''+ bodies - very damaging for the player, but with a significant improvement in sound. Many of those were made by Arthur Richardson. Some of them sound really nice. Other makers tried weird shapes, some with excellent sound, for example Hitzoki Izuka. There is a lot of trial and error research that went into these instruments. Now some makers can build violas of around 16'' with a marvellous sound. 16'' is manageable for most players. Manifio in this forum is such an expert. His violas sound excellent in YouTube sound samples. There are other makers who have also been very successful. I have tried many, one of favourites is a viola by UK maker Piper who tried many viola shapes. Makers need to make lots of instruments until they found their ideal sound. If the viola gets more recognition the taste of sound for this instrument may evolve, maybe differently than we expect.
  2. Are you sure this is not dirt building up? There is no good reason why a black colour (massive absorption) should develop - at least I can't see this at the moment. In some of these Southgerman instruments the black colour is caused by the use of dichromate which is a massive oxidant. Theer the surface of the wood turns black. For which makers have you seen this blackening?
  3. Depends what the solvent is. Turpentine (alpha-pinene) won't give you a lot of fluorescence. I don't know what other solvents you use. Oils won't evaporate.Oil varnish drying is not an evaporation process as is the case for spirit varnish. Try oxygen-free and oxygen-loaded linseed oil. Oxygen is known as a flueorescence quencher.
  4. Fluorescence stands for a spontaneous emission of light after light exposure, whereby the emitted light has a longer wavelength than the original light source. I.e. you shine blue UV onto the varnish and it emits visible light, or you shine UV in freshly washed clothes and you get a white visible light. Fluorescence can be quenched, in varnish, a well-known quencher is oxygen (this quenching effect is used in oxygen sensors). Once all oxygen has been used to cross-link the lipid chains it is chemically bound and the remaining conjugated double bonds will show fluorescence in absence of a quenching substance. Importantly, it is still only those alpha-linolenic acid and linoleic acid molecules that maintain their conjugated double bonds that fluoresce. Those lipids that were cross-linked have lost their chromophores. I therefore assume that what we see shine in varnish is the free fatty acids. An experiment to proof this would immerse lots of oxygen into the varnish - I tried this once and the varnish started to burn immediately. But maybe massive oxygen exposure during drying in the light box could be used as a test. The oxygen would speed up drying but quench the florescence effect. Otherwise an oxygen-free varnish would not be able to used oxygen for cross linking and instead dry through Diels-Alder type reactions. This may be slower but give a nicely shining varnish. Another test would be to modify the oil/ rosin ratio. I assume it is mainly the oil that fluoresces. On the other hand abietic acids also has a conjugated double bond and may show fluorescence of its own, although almost certainly with another frequency shift.
  5. You must be wrong according to Sherlock Holmes who traced a crime by using fluorescing linseed oil. https://bcachemistry.wordpress.com/tag/sherlock/ My assumption is that abetic acid esterifies with the glycerole from linseed oil, and this is what happens when we cook varnish. This process alone is known to make a varnish (see lipid reactions lecture). The fatty acids in lineseed oil then get polymerised when varnish dries as explained in the Sherlock article. There may also be other sorts of reactions which are UV light rather than oxygen induced cross linking (after all violin varnish dries under UV light). Whether the abietic acid glycerol ester cross links with fatty acids I am not sure. There are articles claming that they undergo Diels Alder reactions (although with phtalic anhydride), but also with Tung Oil (Guozhang Ma article). Diels Alder reactions require UV light. The fluorescence arises probably from free fatty acids embedded in the varnish and there are good reasons to believe that this looks different when they are immobilised in a solid. Some of the source of my wisom is attached, but I have collected lots more articles which I can make available should anyone be interested. Biobased-Thermosets_link.pdf 07 Lipid reactions.pdf optimizing-catalytic-drying-of-paints-and-varnishes-case-study-at-smalto.pdf Ma_et_al-2013-Journal_of_Applied_Polymer_Science.pdf
  6. Oxygen dried linseed oil would keep some double bonds which are required for fluorescence.
  7. Dear Michael I think this generally makes sense. I think Woodhosue got an unlucky spot with some minerals underneath the varnish. Maybe Stradivari used some minerals for sanding and some was left. I can't see why you think a lye would make a difference. Echard also used GCMS to proof the presence of the rosin compounds. THe results are conclusive. I still wonder whether he picked up soem left-over monomers, but then he thought about this and used PyGC-MS. The pyrolysis is to break down polymers - a dirty process though.
  8. These are good points. In the polymerisation process not all fatty acids get cross linked. One of the 3 fatty acids from linseed oil, oleic acid, won't do much at all. This means there are fatty aicd molecules embedded in the polymer. This may be the reason for the optical properties of these varnishes. With FTIR I would assume to see the polymer and the free fatty acids. With GCMS one will only see the free fatty acids, the polymer will neevr go up that GC column. What Echard measured with GCMS is therefore probably the free fatty acid content of the polymer.
  9. If you add add a siccative it will even dry fast. These siccatives (e.g. cobalt) simply work as catalysts for oxygen induced polymerisation. This is described here https://en.wikipedia.org/wiki/Drying_oil In the UK gun stock makers used to varnish with just linseed oil. I am however still not sure whether violin varnishes are air dried or light dried as all violin makers use light boxes. Probably a mix of both. Can be measured by weight change - hgher weicht means oxygen induced polymerisation.
  10. It is correct that moisture in methanol is a problem. You can of course buy 99.9% methanol but this a lot more expensive. Particularly during the pandemic it has become hard to get a hold of pure ethanol. Isopropanol is indeed much better in that respect. I have made spirit varnishes with iso-propanol and some makers like it better. You need to be quick with the brush if you use isoprop. Among unbranched molecules longer does indeed mean higher boiling point. But the iso does the trick to lower the bp.
  11. How did they blacken the wood? Lots of dichromate?
  12. It dries just by evaporation of the solvent. Use isopropanol and it will dry faster. The problems with getting hard seem to arise from esterified components of the shellac which you avoid by using a good quality shellac and by dissolving it fresh every time. http://www.michaeldresdner.com/how-and-why-does-shellac-go-bad/
  13. Echard's works on violin varnishes are scientifically among the best I have seen. There are two more I know of. But he never bother to quantify the oil/rosin ratio. Figure 4 in the Angewandthe paper sheds light on this, but peak intensities in GCMS are not particularly quantitative without proper calibration. Nevertheless, if you add all the peaks marked with a round dot vs the P, O and S it looks like a oil/resin ratio of 3/2. It is however possible that his GCMS only measures the unpolymerised parts of resin and drying oil. If drying leads to cross-linked products they would not show up. Echard 2004.pdf Echard 2007.pdf
  14. The Bernardel disappeared some time during the auction.Can they do this, just withdraw? I assume the owners changed their mind or there was doubt whether it was genuine.
  15. I have seen a few violins without value with a great sound. This one sounds great in the hands of this player, even though it is a factory made instrument. I once heard a Hungarian band in a restaurant in Budapest. I then also played a few notes on that fiddlers violin and was disappointed, he had a very simple violin. His bow was even more awful, no strength in the stick. But he was completely adapted to this setup and played a super fast Czardas really well.
  16. I ask questions as Iook at violins out of interest, this doesn't mean I want to bid.
  17. Can I ask for several opinions at one time: Frederick Daniel Mahoney - is he known to any one else? It looks interesting. https://www.bromptons.co/auction/22nd-june-2020/lots/132-an-english-viola-by-frederick-daniel-mahoney-london-1937.html The Bernardel viola (they had this already in the last auction): There are a lot of typical features but some are not Bernardel, the scroll is very untypical, and I hae never seen this varnish on an AS Bernardel. The edge work work of the front is also not typical, and the choice of wood for the front is irritating. https://www.bromptons.co/auction/22nd-june-2020/lots/136-a-fine-french-viola-by-auguste-sebastien-bernardel-pere-paris-circa-1840.html After Gaetano Chiocci: https://www.bromptons.co/auction/22nd-june-2020/lots/137-a-viola-after-gaetano-chiocchi.html Looks interesting, but what is it really? Lots of repairs on this one.
  18. These are very beautiful fittings and they make these nice gold ornaments.
  19. uguntde

    Viola ID

    Who the hell is Harris and Sheldon in the Brompton highlights? https://www.bromptons.co/auction/ Is this Nigel Harris from New Zealand? Somewhat uninspiring with kind of perfect workmanship.
  20. 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.
  21. 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
  22. 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.
  23. 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?
  24. I hope you are not insulted, but the value is that of firewood. The newspaper inside may be worth more though.
  25. 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.