uguntde

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Posts posted by uguntde


  1. 7 hours ago, sospiri said:

    If the oil or varnish goes black as we see in some old instruments and paintings  is this because it is oxidizing without polymerizing?

    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?


  2. 17 hours ago, Michael_Molnar said:

    I’ll hazard a guess that you are seeing the solvent dominating the fluorescence at the start. As it evaporates or dissipates the roasted rosin is left to fluoresce. I’d need to do some simple tests to evaluate that hypothesis. 

    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.

     


  3. On 8/27/2020 at 10:06 PM, uncle duke said:

    I'd put money on sospiri or uguntde having the theory.

    My guess is an ingredient from the tube may have something to do with it.  Mine goes darker with some sheen loss - hope it stays where it's at.

    edit - I use a quart glass jar for holding spirits of turpentine so that it can air out before use for varnish making - I notice the dried out residue on the inside of the jar has the same dullness/sheen that I think I notice on a few of my later violins - [recipe change].

    It is a sheen that is glossier than a semi-gloss from the hardware store but not as luminescent as a violin by Mr. Ouvry that I have. 

    Then there's always the possibility of linseed oil changing everything like Ugun explained above. 

    Fluorescence?  I'm not familiar with what I should know about it- haven't reached my level of incompetence yet.

     

    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.

     

     


  4. On 8/22/2020 at 5:57 PM, Michael_Molnar said:

    Fresh oil doesn’t fluoresce. The aging process develops fluorescence. So, it must not be simply a process of retaining certain bonds, but developing others that either fluoresce or no longer prohibit fluorescence. 

    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


  5. 11 hours ago, Michael_Molnar said:

    Dried linseed oil will fluoresce after it yellows over time. Will this explain the fluorescence observed from the under coat beneath the colored varnish layer? I know that a lean clear varnish fluorescence very brightly. Will a thin linseed oil film do this too? Any research into this?

    Oxygen dried linseed oil would keep some double bonds which are required for fluorescence.


  6. On 8/12/2020 at 10:00 PM, Michael Szyper said:

    Dear friends,

    Finally I arrived at a stage where I would like to share and discuss my thoughts about the following publications:

    • B Brandmair, SP Greiner „Stradivari varnish“
    • J-P Echard, S Vaidelich et al; „The Nature of the Extraordinary Finish of Stradivari’s Instruments“; Angew. Chem. Int. Ed. 2010, 49, 197-201
    • CY Barlow and J Woodhouse; „Of old wood and varnish: Peering into the can of worms“ JCAS Vol 1 no. 4 (Series II) Nov 1989 pp2-9

    First of all, I would like to explain the very basics of the used and discussed methods:

    FTIR: Fourier transformation of infrared spectra. Objects are irradiated by blackbody radiators. The specific absorption spectrums are analyzed and help to identify especially OH, C=O and CH2/CH3 groups.

    Scanning Electron Microscope (SEM): Electrons are fired at an object, a very sharp picture is achieved. Conductive coating and vacuum are needed.

    SEM/EDX: The electrons fired at a sample induce electromagnetic radiation (x-rays) with specific spectra, depending on the atoms. The radiation spectrum is detected and analyzed by its peak distribution. This method CANNOT detect atoms with lower atomic number than sodium. That means, that for example carbon, hydrogen nor oxygen can be detected by this method. (This point will be important later on, since these are by far the main components of colophony and linseed oil)

     

    Let’s start with the naked results without any interpretation.

    1. Brandmair & Greiner

    B&G compared the FTIR spectra of fresh applied varnish made by Stephan Peter Greiner to the Strad varnished. Greiner made several varnishes with different oil:resin ratios. The FTIR of Greiners 80:20 varnish (final and applied product) matched best to the Strad FTIR spectrum. 

    UV and vis microscopy could not identify filler-type particles within the ground layer. SEM pictures were not provided in the book.

    Side note: UV and Vis microscopy can not identify colloidal suspensions of very small particles, they would appear as a homogenic mass. Brandmair also commented about this issue in the pigment chapter.

     

    2. Barlow and Woodhouse

    IMG_0522.thumb.jpg.d4751b254520957339a7a8b01961821e.jpg

    This is the only SEM picture provided in the publication, which can be attributed to Stradivari with sufficient confidence.

    I colored the left side to discern between the different layers. They found a very basic porous layer (red). There are almost no particles penetrating the porous structure. Then there is a ca. 60 µm thick layer (green colored). It appears inhomogenic, with amorphous particles of different sizes between 1 µm up to around 10 µm. A third layer (blue colored) sits on top of that, it is around 2 µm thick and appears quite homogenic.

     

    In the SEM/EDX different minerals were found. Please keep in mind, they can not provide information, if and how much of organic material is in the sample due to the method. So, the varnish/resin content within this particulate matter can not be provided.

     

    3. Echard et al

    IMG_0523.jpg.e271d73b76fd89e4a8e6756a6d771d6b.jpg

    UV-Microscopy shows three different layers. The lowest one being the wood, covered with a green-whitish fluorescing layer and the top layer with yellow-salmon like fluorescence patterns.

    Here are the according FTIR spectra of the three layers.

    IMG_0524.thumb.jpg.a28e52aa443ceeb336e0947462d40482.jpg

    The main difference lies in the OH-band, which is very weak in the lower varnish layer. Echard stated this to be the lower varnish layer, comprising of pure linseed oil.

    My interpretation of the results

    You all know the interpretation of the authors, so I left it out. First of all, let us begin with the SEM picture of Barlow/Woodhouse. They state that the bottom layer (red) is wood, the middle (green) being the particulate mineral ground, and the blue colored stratum should be the color varnish, which was in their opinion almost gone (but they stated about the same sample that it had a striking brownish color).

    If you assume that the middle layer are the varnish layers, the thin top layer (blue) could be a restorers french polish. The middle stratum with around 50-70 µm does not appear way too thin to be a full varnish layer.

    Barlow/Woodhouse did not perform an FTIR analysis on this layer, only SEM/EDX. Therefore, there is lacking evidence against the middle stratum being a varnish layer without a mineral filler.

     

    What if the middle layer (green) would be the actual varnish, for example a cold-combined high-resin low-oil varnish. This would be rather a colloidal suspension of oil and amorphous colophony particles than a solid („firm pill stage“) varnish. You could easily obtain a SEM/EDX spectrum like the one Barlow measured. You still would not know if it is 0,1% Si and 99,9% organic material.

    So, with the lacking FTIR, the Barlow/Woodhouse results could also fit my interpretation.

    Echard et al. In contrast did an FTIR of the base layer stating that this would be pure drying oil. I do not disagree with their results, the FTIR fits (if the base varnish has not treated with a lye).

     

    If I make a cold mixed varnish and put a drop on a paper, the colophony stays where it is, the oil soaks in the circumference of the paper. So the varnish disarranges - drying oil leaves the varnish and soaks into the wooetd. Et voila, here we have the pure drying oil as a base coat layer in the varnish. After the solvent evaporates, the dissolved colophony may form small amorphous particles surrounded by linseed oil.

     

    And what about B&G? They did not found a mineral layer in the base coat and used FTIR AND SEM/EDX. On the other hand, uv- and vis-microscopy would be too low in resolution to show the varnish actually as it is - a suspension of colophony particles and dried linseed oil.

     

    I have the lack of a modeled experiment to approve these claims. I would need to apply cold-combined varnish on a well prepared wood and let it polymerize. After a bit of aging, SEM, SEM/EDX and FTIR needs to be done on my prepared samples. If they would match, this could support my theory. Until then this is not more than a humble theory.

     

    I would enjoy any comment about this.

    Michael

    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.

     

     


  7. On 8/13/2020 at 5:36 PM, Michael Szyper said:

    How can you prove that a layer consists mainly of substance x and not substance y if a method (EDX) is only capable of detecting substance x?

    As I mentioned, what I wrote is only an interpretation - i.e. the same what Barlow did with his data. I would like to discuss the methods used in those papers and mainly their weaknesses, because only then we can interpret the data in a better way. I just find it intriguing that the data provided by the publications is not all that different, but the interpretations does.

    I agree with you that FTIR alone is not sufficient to provide exact resin:oil ratios. Brandmair wrote that the FTIR spectra compared best in the case of 80:20 varnishes. This does not necessarily mean it is definitely a 80:20 mix. 

    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.

     


  8. On 8/17/2020 at 12:01 AM, David Burgess said:

    Oil without any resin at all will dry just fine, and will even eventually become hard and brittle, given enough time, or if exposed to enough sun or UV.

    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.


  9. 13 hours ago, Andreas Preuss said:

    Thanks. Seems you know the chemistry. 

    Actually we used in Tokyo violin making school Isopropanol. However Mr. Murata didn't say it evaporates faster he said it doesn't attract moisture so much. 

    I always thought that the bigger the molecules of the solvent the slower the evaporation process. Seems to be wrong. 

    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.


  10. On 8/4/2020 at 1:25 PM, Andreas Preuss said:

    This is basically a question addressed to people here with chemical knowledge.

    I would like to get shellack quicker hard after application. Are there any additives which can achieve this?

    The shellack I am currently using is the dewaxed quality in flakes. 

    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/


  11. On 8/4/2020 at 7:44 PM, Davide Sora said:

     

    In fact, Echard interpreted what he found in the wood (with a penetration from 30 to 100 micrometers in the maple and from 10 to 30 micrometers in the spruce) as a drying oil, with no added particulates.

    Echard-Stradivari finish.pdf 402.73 kB · 31 downloads

    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


  12. On 6/11/2020 at 11:45 AM, martin swan said:

    Mahoney : this appear to have been stripped of its original varnish. If Three13's Mahoney is authentic (and I don't question it because it's so close to FW Chanot) then we might conclude that this is by a different maker since it has no shared features as far as I can tell. Either that or Mahoney decided to abandon his roots and move into copy work

    ASP Bernardel : a bit surprised at the date but otherwise looks to me to be very consistent with this maker in the 1820s. The scroll has lost most of its inking which changes the appearance significantly. The choice of wood for the front doesn't irritate me at all, in fact I would consider it an excellent starting point for a small viola. Many great sounding instruments have been made with wide grained spruce, but maybe your aesthetic concerns triumph over the desire for sound.

    After Gaetano Chiocchi : looks like a relatively modern instrument - I would think the worm was already in the wood chosen for the back. I don't see any repairs, just a lot of antiqueing ...

    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.

     


  13. 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.


  14. On 6/9/2020 at 3:51 PM, martin swan said:

    Indeed, that's always been one of the quirks of The Auction Scroll!

    Just for the record, I have absolutely no interest in either item, as a buyer or a seller. But you're right that one should be wary of any advice or opinions given here, and suspicious of people who draw attention to items.

    I ask questions as Iook at violins out of interest, this doesn't mean I want to bid.


  15. 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.

     

     


  16. 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.


  17. 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


  18. 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.


  19. 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?


  20. 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.

     


  21. 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.