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John Harte

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  1. 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...
  2. 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..
  3. 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.
  4. 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...
  5. 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.
  6. 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.
  7. 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".
  8. Context is everything....
  9. 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.
  10. 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.)
  11. I'm not sure what hypothesis you are referring to. Are you asking me to comment on Echard's findings or something else?
  12. 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.
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