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Jim Bress

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Everything posted by Jim Bress

  1. Thanks, I’ll have to head down and visit them.
  2. Potassium nitrite is about 8 times more hygroscopic than sodium nitrite based on the limit of solubility. This article may be of interest. The influence of multilayered.pdf
  3. Thanks for the pics. Is this at the American History museum?
  4. The definition for inert varies by country and type of product. However, the general definition of "inert" in consumer products means an ingredient intentionally added that has low toxicity for the intended use.
  5. I used to use coyote urine as a scent lure for wildlife population surveys. Still can't forget that smell. Vilest stuff on the planet. I kept waiting for Mike Rowe to stop by and give me a hand. He never did. Now back to your regularly scheduled violin making discussion.
  6. It's been a journey. I remember Mike Jones forgot the form with blocks installed at a workshop we were both at. I happened to see it sitting in the corner of the room as I was leaving. I ended up driving it cross country to your workshop while I was on other "nearby" business. A nice way to meet a new friend.
  7. I’ve started reading this article and it looks promising. Really I’m just starting the methods section and so far it appears to be well set up to test the questions being asked. I review up to half a dozen research articles a week and it is in the method section that many papers live or die (for my purposes). Sorry John for the slow response.
  8. Just think, I’m another 20 years you’ll be in your golden period.
  9. Thanks for the article. Interesting, but not particularly helpful unless you were looking to either increase or decrease the amount of wood darkening that occurs during kiln drying.
  10. Hi Mike, The varnish is approximately 1:1 colophony:linseed oil. The only other resin is mastic tears. That's it, no pigments or anything else. I say approximately because I don't think the ratio tells the whole story. Certainly mastic tears does not have the same properties as colophony. Likewise, cooked colophony (reduced in volume by 80-90%) does not have the same properties or even chemical structure of uncooked colophony. I have a citation someplace that talks about the compound structure created from linseed oil and colophony will vary depending on the temperature the compounds are formed. Likely the varnish of a given batch is comprised of multiple compounds, but that's speculation. I don't worry about the various compounds because it's something outside of my control. However it may partially explain the variance between varnish batches. My uncolored varnish (not cooking the colophony down) is 50% colophony, 40% linseed oil, and 10% mastic tears by weight. I don't add the mastic tears until the varnish is stable between 95 and 100 C. Too cold the mixture won't incorporate into the varnish, too hot and the mastic tears will boil off. For color, I melt the cooked colophony with equal weight linseed oil and add to the uncolored varnish (before adding the mastic tears) until I'm happy with the color (about 50% of the uncolored varnish volume). Adding the mastic tears increases the viscosity. I add additional linseed oil to get back to the thickness of room temperature honey (ish). So 1:1-ish. I think I have a PDF of Jacksons Scroll article, or at least I have the issue. When I locate it I will send it to you. Cheers, Jim
  11. This is a cut off from the willow cello back that’s part of my current build. Over a year ago I shaped the piece of scrap wood into a door wedge because it was already almost in that shape. I had just finished making a batch of varnish from Roger’s recipe plus bits of information I learned at a few of Joe Thrift’s workshops. I thought a doorstop would be a good stress test for the varnish. A year + of kicking into a door bottom (you can just make out some scrape marks) and the varnish is nearly undamaged. There are places where the wood dented but the varnish didn’t crack, and it won’t take a scratch from a fingernail. I didn’t lime the rosin. Maybe it’s a fluke batch that happens to work. I guess I’ll find out in time. Point is, I don’t think you’ll get all your answers from the ingredients, as the main ingredient is the cook.
  12. Nice to see more of your work, and glad to hear you’re still in the fight.
  13. Head slap! Yes, I chose the model in large part because of the sound. Not that I would be able to reproduce it, but it's a good place to start. The Cello is by Pietro Giacomo Rogeri 1717 https://tarisio.com/cozio-archive/property/?ID=40712 The player of the cello is Enrico Dindo. One of many YouTube videos. Sadly I have never heard it played live. https://www.youtube.com/watch?v=9lIMmE6GxwI I plan on increasing the grads of the back by 50% because it is made of white willow (Salix alba) instead of maple. The ribs are beech. The choice of woods is your fault Melvin because I fell in love with pictures you showed in your bench thread some time ago. The wood is definitely too good for the likes of me, but I'll do the best I can to not make a waste of it.
  14. Would checking %water in your ethanol help with the troubleshooting. Should be fairly simple with a volumetric flask graduated cylinder, digital scale, and a calculator.
  15. Most folks that have been here a while know John (violins88). He makes darn good knives for makers. Well, that’s half the introduction.
  16. Hi Melvin, Yes the strad poster has grads. Somewhat thinner than J. filius 1710 cello of nearly the same bout widths, but unknown arching. The Rogeri has quite full archings so the thinner graduations make sense. The top is a bit more of a mystery as there are no grads under the finger board or the tail piece. Although I would guess slightly thicker along the center line. I'm just not fond of guessing (occupational hazard). At present, I'm taking the greater of the asymmetrical thicknesses and adding a couple of tenths of a mm for my first rough gouging.
  17. Crickets... To be clear, I'm not asking about the thicknesses. Rather the pattern of the thickness map. As I said before, the biggest difference seams to be the pattern for the top where Sacconi uses a constant thickness, whereas Brian Derber's diagram has a more complex (concentric) pattern.
  18. I'm at the point in my cello build where I'm preparing to graduate the top and back plates. The cello is based of the Strad poster for P.G. Rogeri 1717. I've increased the LOB to 746 mm by rounding the neck and tail block areas of the outline. My bout widths are 353 mm, 243 mm, 440 mm. https://www.thestrad.com/lutherie/from-the-archive-a-1717-brescian-cello-by-pietro-giacomo-rogeri-/7878.article My question is in regard to what graduation pattern folks use that make cellos of this approximate profile (also similar to filius Andrea Guarneri celli). Without knowledge of whether the instrument had ever been regraduated, I hesitate to simply try recognize the graduation pattern (without following every dip). The graduation pattern maps I have for cello are from Brian Derber's book, and Sacconi's book. The biggest difference between the patterns to my eyes is for the top plate. Thanks, Jim
  19. I had not heard of diamond willow before. Is this what you are referring to? https://en.wikipedia.org/wiki/Diamond_willow and this https://www.wood-database.com/diamond-willow/
  20. What is "hard willow beech"? Or do you mean willow or beech of relatively high density for each species? Thanks, Jim
  21. I think it's very nice looking, but it depends how far down the rabbit hole you want to go (sorry to be the dissenting voice). If you were making an entire instrument, I would say that you still have too much color in the wood. Your "flames" fade and reappear, but they do not move. The other thing I look for is the illusion of depth. Here's an idea of what I'm talking about from a MN search. This wood isn't even finished yet. Good varnish and application should enhance what you have from well prepared wood. https://maestronet.com/forum/index.php?/topic/329780-intriguing-maple-back/&do=findComment&comment=610710
  22. It’s a good happy accident then. A little Girolamo (sp?), plus a little Chris!
  23. Very nice. I like the f’s a little better than what I usually see on N. Amati’s. Did you add just a smidge to the wings?
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