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John Harte

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  1. Only if it includes callus resin. I am referring here to Norway spruce.
  2. It is relatively easy to make a workable varnish using spruce oleoresin that behaves in much the same way as a pine resin varnish. Spruce callus resin should be avoided though.
  3. Yes some form of stain could well be involved. At least some wetting of the wood structure with varnish or similar seems important in achieving the type of look seen in my photos. Other factors like wood ageing etc., etc., also seem to make a difference.
  4. Joe (and Mike) I was hoping you wouldn't see my post... Five reduced size photos are posted below. Each is labelled, indicating instruments involved and the direction of the point source incident light. The first four photos feature spruce while the fifth, maple. Maple is a more complex situation due to the undulating nature of the fiber direction. Of note in the first two photos is incident light focused along the grain resulting in the medullary rays/plates at right angles to the incident light strongly reflecting light. In a relative sense, most of the other wood cell structural detail seems absent. In contrast to this, the next two photos illustrate the effect of light focused across the grain. Here the along grain structural detail reflects light while the medullary darken/appear absent. If spruce viewed under a point light source is rolled relative to the light source, it is possible to see the various medullary effects at different levels move relative to one another, creating a sense depth. In maple, not only do the medullary appear to move relative to one another, but the undulating fiber direction and how it reflects light or not creates the light and dark areas that we see as flaming. The final photo below featuring a section of maple hopefully suggests this. I hope that this all makes sense and does illustrate that it is components of wood cell structure aligned towards or at right angles to incident light that reflect light. I may be able to find some photos to illustrate the extent to which light can penetrate wood structure, but that will take a little longer than this.
  5. Light enters far further than 7 microns. Based on my own observations I suspect up to 6 cell layers deep. Each cell is approximately 30 microns wide so that's quite some distance. I agree with your second sentence quoted above. Interestingly it seems that it is the components of wood cell structure aligned towards or at right angles to incident light that reflect light. I can possibly post photos to illustrate this if you are interested.
  6. While pinaceae resins are an identified common feature in old instrument varnishes, amber presence is yet to be dismissed. I'm not advocating the use of amber in any form, just that, at this stage, no one appears to know one way or the other...
  7. I certainly agree regarding the effects of controlling the temperature and weight loss. I used to sort amber pieces based on colour but in recent years have been lazy especially when using amber from suppliers like Kremer where there always seems to be a mixture. My impression is that time taken to reach the temperature where the amber begins to run is of some importance. In my case slowly heating the amber up to what should be a running temperature has resulted in the resin sweating and not running, ultimately producing a carbonised result that is useless. It might also be that heating up the amber too quickly has certain negative outcomes in terms of transparency and lightness of colour. When attempting to run mixtures of amber resin, it seems that some pieces run more readily than others. Getting everything to run requires pushing the temperature higher which in turn produces a darker end result. Once I get the majority of a mixture running, I try to keep everything bubbling away at that temperature, cooking no more than maybe 15 minutes. Cooking beyond this pushes the colour of the run resin towards an increasingly cold looking and deeper/darker brown. (You can check the development of colour via placing blobs of resin on some glass, noting how the colour changes with cooking time. Be aware though that thermal shock can/will readily crack the glass so try to somehow keep the glass reasonably warm!) The downside of this is that you end up with lumps of amber that haven't run in amongst the run resin. In the spirit of laziness I haven't worried too much about this as these lumps are in the minority and get filtered out during filtering of the final varnish. Re fire mentioned by charliemaine, the very few instances of volatiles igniting that I have experienced have all involved the use some form of wind shield. I would also make sure that there is at least some breeze present when running amber..
  8. Mine did that at the 1994 competition. Had two weeks for varnishing prior to jumping on the plane to get to the U.S... Even the plush velvet lined case left its mark.
  9. Evan, thank you for your photos and very interesting replies! I wonder whether the acetone modified the resin and/or oil in some way that resulted in the slight opacity and more during the drying process(???). Also Alkanet is pH sensitive and maybe the pH of the resin and/or oil content had some gradual effect(???). It would be interesting to hear what knowledgeable chemists on this forum might think. As for your second experience, seems like whatever was in your Japan drier worked in very mysterious ways! Maybe the heat provided energy enough for something like iron in the drier to react with the resin in some way.... I can certainly relate to what you mention regarding note taking or not. Too much to try, so little time...
  10. This is interesting. Was the alkanet there as a wood stain or a varnish colourant? From memory I have only tried alkanet in linseed oil and it faded back to almost nothing, but that was a while ago. I'm not sure what the actual linseed oil might have been and whether it would have been put in the UV box or exposed to sunlight or left lying around in my workshop.. My best guess is that one of the first two options would have been involved.
  11. Both true, depending on what you use and how, at least in my experience... Another benefit from not using UV or high intensity UV is that lake pigments tend to fade less.
  12. There may be some confusion here. Firstly, Stradivari wasn't alive in 1638. Secondly, the quote on page 177, while originating in Cremona, seems to come from a letter written by a Father Micanzio that was one of several coming under the umbrella of Galileo correspondence. (See footnote on page 177 which refers you to Chapter XI.) A translation of the actual letter appears on page 242 (Dover edition) under the heading "A fourth letter, dated Venice, April 24th, 1638". The Hills go on to state that while the Cremonese violin-maker's name is unmentioned, they "cannot but assume that he was one of the Amati family, - most probably Nicolo".
  13. Context is everything....
  14. Strad's varnishes may not have required direct exposure to sunlight to dry. Both lead and manganese are a common theme in his varnishes. While a light box or sunlight certainly speeds things up, in my experience varnishes that include lead and manganese will dry in a workshop situation.
  15. This is far too broad to discuss in any coherent way. Even discussing what researchers considering old Cremonese varnish systems have found in the last 20 years is hugely fraught. Making sense of each individual study, the nature of the sample material and the analytical techniques involved and what they are capable of detecting or not is hard enough. Origin of sample material is fundamental and having micro-sample material has advantages. Echard has been particularly well placed in this respect. While Echard's findings may seem to be at odds with other research findings, reading his various studies and those of his colleagues and students can soften this impression. I suspect that there is still a lot to discover in terms of what materials might or might not be present in old Cremonese varnish systems, where they are situated and in precisely what form. And then there is the issue of how they might have got there. (Application methodology and subsequent history is hugely significant.)
  16. I'm not sure what hypothesis you are referring to. Are you asking me to comment on Echard's findings or something else?
  17. See: https://heritagesciencejournal.springeropen.com/articles/10.1186/s40494-020-00460-6 Also see: https://www.sciencedirect.com/science/article/abs/pii/S0584854796015960 The latter includes TXRF data for a number of instrument varnishes including an Amati c.1560.
  18. Once you have created your lake pigment the colour is pretty much locked up. I say "pretty much" as things will happen once it is mulled into an oil or varnish. These pigments almost always fade, at least to some extent, and the mechanisms via which that happens seem complex. Some purples will move to a red-brown or insipid pink or even to a semi opaque brown. Photo bleaching and pH of the varnish will be players along with other factors including the degree to which you have washed your pigment thoroughly or not...... Changing the colour of your lake pigment is best achieved at the point where you are extracting the dye from your dyestuff material; i.e, prior to forming a precipitate. I have mostly acid modified cochineal dye using citric acid, moving colour more towards a red. I also occasionally use cream of tartar as a modifier as part of processes. (This apparently dissociates into acid tartrate, tartrate, and potassium ions in water.) Also using tin chloride mordant as opposed to alum will push things more towards a red, but, in my case, for some reason resulting in pigments that were less transparent. Below are photos I happen to have of some cochineal based pigments that I have made. Some have been happy accidents and some not... (I say accidents because there are so many factors that influence what you end up with...) Perhaps unwisely, I always initially make up relatively small samples until I have some idea of what is resulting in what. At least this way you don't end up with "loads of stuff" that you will never end up using.
  19. See p.8 etc., in this paper: https://www.sciencedirect.com/science/article/abs/pii/S0026265X19321204?via%3Dihub Also see: https://www.spectroscopyeurope.com/article/surfing-through-coating-system-historic-bowed-instruments-spectroscopic-perspective If(???) some form of gypsum is indeed involved, it could well be in a form other than POP. Not a violin study but may still be of interest: https://link.springer.com/article/10.1007/s00339-008-4449-7
  20. Deo, there are good comments in the above posts worth taking note of. Have you tried your lake in varnish yet? Chances are that it will look somewhat less "wonderfully violet" once in a varnish. There are a number of factors that can influence what you end up with. The order of extraction (i.e., alkali first versus acid first), pH values, molar strengths, temperature at various phases during the process etc.. If you are first extracting the dye from cochineal using sodium carbonate (as opposed to using potash alum), you could try acid modifying the dye bath. This can make a difference, as can the particular lye itself. If you ultimately decide you want a lake that is more red, try madder.
  21. Very true! And the involvement of a mordant as in pigments is no guarantee of colour stability within varnish systems. (I haven't got a lot of experience making pigments derived from lac and brazilwood so can't really comment on whether they are significantly more susceptible to environmental pH or photobleaching effects etc., than those derived from madder or cochineal. I can say that in my experience the latter are certainly a minefield...)
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