John Harte

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About John Harte

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    West Melton, NZ

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  1. John Harte

    Don Noon's bench

    Congratulations Don! Well done!!
  2. John Harte

    Any Cremonese Basis for Colored Rosinates?

    An article "The Real Thing" by John Dilworth that appeared in the October 1984 Strad magazine details analyses of several old Italian violin and cello varnish samples carried out by Raymond White. Quoting from this, "White was quite firm in ruling out both Michaelman and Fulton theories in three particular examples. The metal soap rosinates of Michaelman varnish are apparently very distinctive and would have been easily revealed by these analyses."
  3. John Harte

    The ground ( sealing) of the great masters - which was it ?

    I'm not sure that succinic acid presence can be considered a viable marker for amber varnish. Succinic acid has a relatively low boiling point (235°C) which would make it likely that any presence would be eliminated during open pot cooking/running of amber. It seems that the only usable marker for amber presence is Δ 8-isopimaric acid, but there are problems... As Raymond White has pointed out, "Amber has a very low amount of characteristic diterpenoids, the major component of which is Δ 8-isopimaric acid. In favourable cases this might still just show up. However if amber were incorporated with just one tenth of its weight of rosin, the latter's diterpenoids would swamp those of amber." (Raymond White: "Eighteenth Century Instruments Examined", The Strad, August 1984. pp. 256-259.) It seems that there are similar issues with identifying run copal within varnishes.
  4. John Harte

    Extracting a yellow pigment from aloe

    The only study involving Andrea Amati varnish that I know of is this: https://www.researchgate.net/publication/222897899_Microanalysis_of_old_violin_varnishes_by_total-reflection_X-ray_fluorescence An earlier version of this featuring the same element data can be downloaded here: https://www.researchgate.net/publication/297350011_Arsen_und_Blei_im_Geigenlack There are other studies featuring Girolamo and Nicolo Amati varnishes. From what I recall, none (the above included) have identified arsenic in an Amati varnish. This sample size is very small though......
  5. John Harte

    Extracting a yellow pigment from aloe

    David, thank you for this. I was aware of Barlow and Woodhouse and maybe one other study having found arsenic in Strad varnishes but don't recall its mention in recent studies featuring Amati varnishes.
  6. John Harte

    Extracting a yellow pigment from aloe

    If at some stage in the future you again come across this study, I would be interested in knowing what it is.
  7. John Harte

    Extracting a yellow pigment from aloe

    Orpiment is also available from an art material supplier in London but, as Christian mentions, it's too scary. I also don't recall any mention of it having been found in any of the Amati varnishes that have been analysed. Weld (Reseda luteola) produces a useful yellow. ( Extract dyestuff with alkali, e.g., potassium carbonate and precipitate with alum.)
  8. John Harte

    Stradivari's secret was a concept?

    Re alum treatment of wood, some caution may be appropriate. If you google alum treated archaeological wood, some interesting studies come up.
  9. John Harte

    Working with pigments

    Thank you Urban Luthier! These are superb!
  10. John Harte

    Corner geometry question re Guadagnini, observations.

    Stephen, if you have access to past VSA Journals it might be worth taking a look at the transcripts of Roger Hargrave's lectures in Journal Vol.10 No.2 ("Classical Edgework") and Journal Vol.13 No.1 ("Instrument Recognition"). These contain some excellent detail relating to J. B. Guadagnini.
  11. John Harte

    Mr Alf's letter to Vuillaume: recipe for Strad's varnish?

    Yes this would be very interesting. The nearest I am aware of appears in this publication: https://www.scrollavezza-zanre.com/la-viola-girolamo-amati-monografia/
  12. John Harte

    Mr Alf's letter to Vuillaume: recipe for Strad's varnish?

    Echard has mentioned penetration in maple up to 100 microns and up to 30 microns in spruce. (Re spruce, one of his microscope images suggests localised greater penetration than the mentioned 30 microns.) Other studies mention similar. Microscope images of samples in "Stradivari Varnish" by Brandmair and Greiner clearly show varnish in wood cells below the region exhibiting a protein presence. Included diagrams illustrating the observed layering of the varnish system also illustrate this.
  13. John Harte

    red flames

    Re the two shots that I have posted above, if you look closely you will see that the positions of dark flaming/light wood in between are reversed in each shot.
  14. John Harte

    red flames

    Mike, Attached are a couple of shots of a golden period Strad. The same camera and camera settings have been used (aperture, shutter speed, white balance etc.,). The first shot was taken indoors under a combination of indoor ceiling lighting and window lighting. The second shot was taken under outdoor light (mid afternoon, full cloud cover). I apologise for the lack of clarity in these reduced size files. The full size files are much better. Even so you will see the effect of the different lighting. I suspect that the flaming would look even more red under direct incandescent light. John