uguntde

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About uguntde

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    https://www.birmingham.ac.uk/staff/profiles/cancer-genomic/gunther-ulrich.aspx

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    Science, NMR, string instruments

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  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.