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John Harte

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Everything posted by John Harte

  1. I agree. Not so much of an issue here, but many violin varnish studies also appear to suffer from confirmation bias, either in employing starting points based on questionable prior studies, or interpretation of their own data that is, for various reasons, somewhat limited in its scope.
  2. Maybe this adds something: https://www.researchgate.net/publication/319672461_Reconstructing_historical_recipes_of_linseed_oilcolophony_varnishes_Influence_of_preparation_processes_on_application_properties More detail here: https://www.researchgate.net/publication/320555276_Proprietes_physico-chimiques_et_vieillissement_des_vernis_huile_de_lincolophane_de_la_technique_du_luthier_a_la_conservation_des_instruments_de_musique_vernis
  3. Thanks for posting these photos. I thought I was seeing something in your original photo that is actually not the case.
  4. Thank you for your reply. It would be interesting to see a photo of the other bridge.
  5. Rustle, did you cut this bridge?
  6. A more recent related study: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8446710/
  7. Taking a shot under a single source incandescent light may provide more contrast. Even a torch with an older style wire filament bulb should suffice.
  8. It is SO complicated!!! Some aspects will also appear to darken and/or become more transparent/translucent or opaque with significant optical consequences.... And yes UV fluorescence can change over time, or not much.. Research still has much to offer even though various markers will have changed or disappeared over time. I wish researchers would engage more with people like you!
  9. Melvin, what you do is stunning!! I agree with what you say regarding UV light and, for that matter, comparison under as many different forms of lighting as possible. Your theory regarding no end grain darkening is very interesting. I can't say that I have experienced significant issues with end grain darkening but am probably missing something. Below are a couple of shots of the spruce sample shown earlier but this time without the end grain area cropped out. What was applied to the quartered face was also applied to the end grain area. (Both shots were taken under the same single incandescent bench light but with the light direction changed between each.) While I don't antique, I have a colleague, who uses a similar varnish system, who does. He doesn't seem to have issues with end grain darkening but, again, I am probably missing something...
  10. No size. Same basic process for maple and spruce. Some slight blotchiness is inevitable when applying the stain to spruce but with a little care during application, this can be largely avoided. Once a top is fully varnished, any initial blotchiness is barely noticeable, and, if anything, subtly adds to overall complexity. The stain I use has only moderate colour value. It helps to enhance certain things like introducing a reddish aspect seen under certain lighting conditions but overall is fairly subtle in its effect. As with certain other stains, even heavy applications don't result in grain reversal which, of course, is a situation best avoided. Unfortunately I don't have any photos of an entire top with stain etc..
  11. The first shot was taken under a single incandescent bench light. The left third is stain over wood that has been exposed to UV while the right two thirds features an added very thin almost colourless oil varnish coating. The detail here is much better than the photo suggests. The second shot features an old sample taken a while ago. This shows the degree of detail that you can see in the first sample when looking through a 20x magnifier using a more directed/focused light source.
  12. In this particular case madder is involved but other reds can work equally well, if not better. Be wary of my photo. While there is a genuine reddish aspect that is not photo artefact, there are a number of things that are going on. One is the colour temperature of the lighting, another the fact that single source lighting is involved at a relatively low incident angle, another the optical effect of the oil varnish within and above the wood structure etc., etc.. With respect to the varnish, the cooking process(es) can obviously contribute a reddish aspect. The photo below shows a little more than my initial photo. The wood to the right of the varnished areas features the stain which almost looks like nothing.
  13. I agree. How a ground looks on spruce is another good test.
  14. Thanks. The last 40 years of messing with this stuff have mostly been 1 step forward and 10 backwards..
  15. Jim, I'm probably going to dig a massive hole for myself here... There are a lot of things that I look for in what I suppose could be broadly considered ground. One is the ability to see into wood structure and clearly see detail which, in turn, seems related to how structural detail reflects light. Blurred or veiled detail usually seems to dull the type of reflectivity that I am wanting to see. The degree of transparency within the wood structure and depth to which you can see into the structure and the degree of contrast at various incident light angles between those structural elements that reflect light, and those that do not, seem important in achieving a certain sort of look that I find appealing.
  16. Unfortunately I only have close ups of some samples from a while ago. The shot below was taken recently under a single incandescent bench light. The bottom mid to right is ground (UV plus stain followed by clear oil varnish.) What I'm doing now is probably slightly less veiled looking but it's hard to tell as each piece of wood behaves differently.
  17. I suspect that the oil in the upper cells that you refer to relates to a comment in the section covering the Rombouts sample. Here B&W mention, 'There is little sign of penetration of the wood by the varnish. The area labelled “oil” in the schematic is something which has been seen in a number of samples. It closely resembles the residue seen just below the surface of (newly-prepared) wood which has been treated with linseed oil. Doubtless other oils could leave a similar-looking residue.' I do recall the study you refer to. It wouldn't surprise me if particulates like pumice were present in these varnishes. While it may act as a drying agent, there are also other reasons why it could be there. In terms of drying agents, lead and manganese are another possibility, being a common theme at least in Strad varnish systems. See: https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/abs/10.1002/xrs.2825
  18. The below are comments with particular reference to the Barlow and Woodhouse (B&W) study and my own viewing of various varnishes under Scanning Electron Microscope (SEM). I should preface these comments by stating that I believe that Barlow and Woodhouse's work remains highly significant and don't believe that published comments by Brandmair and Echard are necessarily at odds with their observations. It, to some extent, comes down to interpretation of what has been observed. 1. There are various varnish formulations that, when viewed under SEM, can look like they might contain particulates and yet do not to any major extent, e.g., a thick casein layer, various emulsions, certain very short oil varnishes. Under SEM these can look quite porous and crumbly. 2. When viewing varnish layers under SEM, certain sizes/grounds beneath these layers can "disappear". I have had the experience of viewing varnish samples under SEM that I created and not being able to see certain applied sizes/grounds that I knew were present. 3. Oil varnishes containing pigments viewed under SEM do look like they contain particulates. 4. From what I can see, the B&W particulate layers generally relate to material "on and above" the surface of the wood. Echard and Brandmair clearly show the presence of material having penetrated the wood structure, which to me, begs the question as to whether B&W's observed particulate layers are in fact a "ground" layer. 5. Jim Woodhouse has commented that the basis of the term "ground layer" occurred as a consequence of John Dilworth and Charles Beare referring to a "yellow ground". I am not sure whether this yellow refers to varnish observed under natural light or UV light. Either way, this is a too simplistic view of how ground appears as opposed to full varnishes. In my opinion B&W's samples do, in some cases, almost certainly include more than just grounds or ground layers. 6. I don't agree with B&W's interpretation of the layering in their SEM images. They invariably refer to very smooth homogeneous upper layers as varnish which IMO is likely polish. The particulate layers below are referred to as ground. These appear, at times, to be 20 - 40µm thick (and maybe thicker) which is far thicker than what Echard or Brandmair have noted the initial Strad varnish/oil size/layer as measuring. From my own experiences of looking at varnish under SEM, layers that are this thick are substantial, far thicker than any observable initial coating on any Strad that I have ever seen (i.e, as seen under visible light or UV). 7. With specific reference to the various B&W SEM images of Strad samples, the particulate layer thickness (i.e., material depth sitting above the wood surface) in the Strad violin varnish sample appears to be in the region of 65µm. The particulate layer thickness (i.e., material depth sitting above the wood surface minus what appears to be surface polish) in two other images of Strad varnish appears to be similar in one and slightly less in the other. (I suspect that these relate to one or both of their Strad cello samples.) 8. Of the 15 or so samples that B&W studied, they found particulates in about half the samples. From what B&W have published, we know that the Strad, Gofriller, and Rombouts samples contain particulates but the Amati does not. The Rombouts (early C18th) and Strad (1711) samples featured in SEM images in the their publications are from cellos, which, at that time, were typically highly coloured. The F. Gofriller sample (1720) was from a bass which was also likely highly coloured. 9. Of note is the opinion of various restorers that the particulate layer that B&W refer to is merely pigmented upper varnish.. I hope that this provides some clarification of my earlier post.
  19. As with most of these situations, maybe not quite as different as might be imagined... The Barlow and Woodhouse particulate ground study was possibly the beginning of this but their interpretation of their data needs context. When you consider the data itself, it's probably not at odds with what Brandmair and Echard found, or rather didn't find.
  20. Yes exactly, it is personal. I wouldn't say that what I use is perfect, merely my go to for purfling at the moment. I do use other knives including options similar to what Jackson mentions. It all depends on what is encountered along the way. While what I am able to achieve is reasonably tidy, it is not in your league.
  21. Blade dimensions: 8mm wide, 1.44mm thick. Length of blade protruding from handle 25mm.
  22. I've tried many and varied knives but have ended up with the below profile. While it might be hard to imagine this working well, it actually does. Amongst other things, it is possible to make both pull and push cuts which can be helpful especially with spruce.
  23. Thank you for your reply. Again very interesting. A number of varnish systems dating from this era have been studied. Most recent studies seem to have been non invasive, the paper you attached to your post being an obvious example. Micro-sample material is obviously potentially more informative than what is possible in situ, but less commonly available. Even so, Strad micro-sample material has been studied by the likes of Brandmair, Echard and members of the Arvedi Lab group. I don't doubt the data presented in the paper that you have attached but find the interpretation of the data related to protein presence presented in the Conclusions section to be somewhat speculative. The contrast between what the researchers suggest might be involved in the Tuscan Strad varnish system and that presented in one of their later papers is interesting. See: https://www.sciencedirect.com/science/article/abs/pii/S1386142520309057 It seems that none of the researchers that I mention above have actually found evidence of a discrete protein based film forming layer in Strad micro-sample material. In contrast, Echard and members of the Arvedi Lab group have both found such in various other varnish systems from broadly the same era. The above referenced paper includes examples. There seems to be more to discover, at least in terms of some old varnish systems. Even in the later paper that I reference, what the researchers mention regarding the nature of the protein presence in the case of Strad remains speculative.
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