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AsaBB

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  1. I have learned that ferric sulphate was used traditionally as a stain on 'harewood', an 18th century term for figured maple used in marquetry. Still, it appears that in solution, ferric sulphate has a pH of about 1, while KOH is around 10. This means they would not exactly end up neutral. mdaddona, in your trials, did you also employ alternating applications of acid then alkali?
  2. This thread may well be dead, and I fully understand that chemical treatments can be a fool's errand... but I am curious on the process Mr. Diaboli and mdoddana are employing. So you prepare a solution (in alcohol?) of KOH, and a separate solution of Ferric Nitrate, and allow time between these coats? And is the aim for these to neutralize each other?
  3. As a longtime quiet Maestronet observer, I have often found Neil's contributions to be kind, wise, and invaluable. This is a noble and heartfelt project. I look forward to keeping up with this thread!
  4. Thanks for the feedback. Yes, I do believe seasonal changes have played a part. The instrument itself is not too old either. The action has come down a bit. I remember having the A near 5 and the C at 6.something. I should have written them down. I have been taught to keep a range of 4 to 5.5 for the A and 6 - 8 for the C depending on model and strings. I don't see loads of cellos though, so feedback is appreciated. Nathan, what are your accepted ranges?
  5. Greetings, I am a longtime reader and not much of a poster, as so much is already written! I have searched as best I can, but am looking for general perspectives on the subject of bridge height amendment. I realize there is only one ideal, which is never to adjust or amend. When faced with a rather lovely fresh bridge that was set with an aggressive string relief only to find the customer has become dissatisfied and would now like it raised slightly, will I be forced to make a new bridge, or is there any allowance for shimming from the foot? This is in regard to a cello bridge. The clearance from the fingerboard end is 4.3 at the A and 5.7 at the C. It plays well but can occasionally buzz on the C when targeted aggressively. Beyond the personal circumstance, I see little example or precedent for shimming, and am curious how the professional community views it. Thanks, all.
  6. Depends what you are looking for! I bought their small F clamps for $2.99/piece, and they are fantastic. Anything with electronic or mechanical complexity is another matter. When the same clamp cost $18 anywhere else, however, I will advocate for Harbor Freight.
  7. Kremer describes the acid number range of their common colophony as 162 - 178 mg KOH/g. I am learning how this categorization works. To quote WIkipedia: In chemistry, acid value (or "neutralization number" or "acid number" or "acidity") is the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of chemical substance. Soda lime contains ~1% potassium hydroxide. Other components of lime include sodium and calcium hydroxides. I am not sure how these chemicals interact with the acids in the resins, but hopefully these number help lend some sense to the process.
  8. Kremer gives an acid number range of 162 - 178 mg KOH/g for all common colophony resins derived from various pine species. I don't have useful sense of this kind of measurement as it compares to pH. It doesn't sound like an extraordinary range. Can someone more versed in such language give a layman's comparison? Is linseed oil acidity measured with pH, as it occurs in liquid state? If so, it should be easier to measure the effect washing has.
  9. Don, Will this be the resin collected in Maine, presumably from red spruce? I will be interested to see the results.
  10. I don't talk like that in person! Late night research get's the best (worst) of me. Basically, no point talking about pH! It's the wrong system of measurement for the acids we are dealing with. However, the concept is similar enough, so use your good fiddle-making instincts and neutralize your acids when cooking, or not, because none of the acids we are dealing with are particularly strong. Right? Maybe? Ok, goodnight!
  11. Right, so pH only measures ionic activity in a solution with water. Abietic acid is not soluble in water. Organic acids are considered to have acidic properties, meaning they tend to give away their protons. So in discussing varnish, we are in a murky area involving acids that are only soluble by solvents. The pH measurement process is a product of the Arrhenius Acid definition, which specifies acids by their solubility in water. There are two independent definitions that expand the nature of an acid. Brønsted-Lowry acids are substances which give up a proton to a base. Furthermore, Lewis acids react to a base by way of electron pair transfer. The last definition acts as an oxidizer. Are the organic acids in tree resins Brønsted-Lowry acids, Lewis acids, or both? They are not the Arrhenius acids which are measured by pH. I am spouting off readings. My capacity for chemistry is limited beyond this. From a practical standpoint, non-Arrhenius acids can be altered by the presence of a base, and therefore react in a similar manner to our familiar water-soluble acids. So measurement is tricky, but intuition guides one to stabilize the resin acids by addition of lime, or a similar base. Are there other systems of measurement than pH?
  12. Is there any consensus on an average pH for varnish? Are they generally neutral? Certainly these mineral grounds would have a pH effect. However, Roger Hargrave's slaked plaster method is pH neutral, by nature of the slaking process.
  13. Indeed. It seems like that plateau that David mentioned is real though. Once the color stabilizes, further UV treatment ceases to create a noticeable effect. I had wondered about more aggressive treatments, such as ozone, on finished instruments. I know there's debate as to it's efficacy in general. Just wondering if it would have any effect on cured varnish. Playing with fire, I know.
  14. Any experiences on color stability on a fast, hot cook VS. a slow, low cook? My limited experience, mainly with varnish from resin cooked slow and low, is that the color changes a lot in the first year or two after application.
  15. A friend who is trained in the 19th century atelier method of fine painting pointed me to KAMA pigments for the finest quality Canada balsam. It's his preferred resin for use in oil mediums, due to it's clarity and color stability. He's taken resin from the balsam fir, which is an easy tree to spot here in Maine or most anywhere north of the border. I think it reaches all the way to Alaska? Christmas trees! You can buy some here: http://www.kamapigment.com/store/index.asp?lang=1&catpage=2420 Red when cooked? I would love to see varnish samples! I may have to venture out and collect some.
  16. So can it be said that the color produced from cooking resin is purely the result of oxidization? Some resins are more heat stable than others, yes? Canada balsam, for instance, is said to be highly optically stable over time (with little color change) but has little thermal resistance. Would such a resin be more reactive to cooking? Has anyone cooked Canada balsam? I imagine the optical clarity would be desirable, but I haven't played with it enough to know.
  17. Hi all, New to posting here but a longtime viewer! I am a Maine native and what you typically see in the southern half of the Maine coast is Red Spruce (Picea Rubens) which is eventually replaced by White Spruce (Picea Glauca) further downeast. Balsam fir is also quite common (Abies Balsamea). I've never had a particularly positive experience with any native regional woods here for building, but then, I do not have a lifetime of experience at this yet. Lots of lovely rock maple, and lots of happy mandolin makers. Did you cook any of that resin into a final varnish? Results?
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