Richard Jernigan -> RE: surface (Jan. 17 2017 18:50:47)
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quote:
ORIGINAL: Ricardo Now can someone explain again the difference between Laqcuer, Polyurethane, and Nitro and how to tell difference on a guitar? Here is part of an email I received from Richard Brune, after I had mis-stated that the Arcangel had a lacquer finish: (The rest of the email was on a different subject.) "I saw your comment on the foro re the Arcangel which you mentioned "has a lacquer finish." I wanted to mention that it is NOT lacquer, but catalyzed polyurethane, which is a VERY different kind of finish, much tougher, not prone to age related degradation, and a whole different class of chemical composition. LACQUERS dry by evaporation of high aromatic hydrocarbon solvents (toluene, Xylene, etc) leaving behind a film of nitrocellulose along with other typical additives. To keep these from being too brittle manufacturers add plasticisers such as castor oil, or vinyloids and so on to allow for some film flexibility. Eventually, due to sun, oxygen and other chemical reactions combined with eventual off gassing of trapped solvents in the film, the film will shrink and the plasticisers become more brittle, leading inevitably to crazing, checking and other manifestations of this degradation. In my opinion, nitrocellulose lacquer is a very poor finish for musical instruments due to its inherent tendency to degrade with time. Catalyzed polyurethanes used in Spain and most of Europe are comprised of two separate parts, a varnish which is based on polyurethane chemistry (longer molecular chains), and a catalyst which is added and mixed just before spraying. While there are also present high aromatic hydrocarbons for solvent (to allow flow out), the evaporation or presence of these solvents has nothing to do with the final properties of the cured film which once set becomes nearly inert. Furthermore, this class of coating can be engineered to have different properties of hardness, flexibility, build and etc. It also requires considerable knowledge and technical skill along with appropriate equipment to mix and apply, which is why it never caught on in the American musical instrument trade, whose factories preferred to hire workers of barely simian intelligence. In Spain, most shops do not apply these catalyzed urethanes in house, they send them out to specialist finishers, just as before the war the makers would have specialist french polishers apply the finishes. Once cured, catalyzed urethanes are impervious even to the original solvents used to flow them out during the application process, whereas lacquers will re-dissolve in their original solvents. There is a lot more to the whole varnish issue (polyesters, ultra violet curing varnsihes, etc) which I won't go into here but suffice to say, your Arcangel is NOT a lacquer finish. Its one of my pet peeves when I see other dealers who mix up these two finishes when describing inventory on their websites, it shows a total ignorance of the lutherie side of the business which they should know, and it is deceptive to informed buyers, who seeing a finish described as a "lacquer" (when in fact its catalyzed polyurethane), are going to assume the instrument must have been refinished. Arcangel used several different finishes as "original" including sending instruments out to be sprayed as was the case with yours, so it is quite possible to see very distinctly different finishes on guitars by the same maker, all of which are technically "original." One of the old issues of Jaleo magazine had an extensive interview with one of the guys in Madrid who was a "pistolero" (sprayer) for many of the different makers including Ramirez, whose own shop also sprayed this material, but did not have sufficient capacity to handle the annual production of nearly 1000 instruments/ year they were producing back in the late 60's early 70's. And yes, the type and amount of finish applied and skill of the sprayer can have a significant affect on the outcome of the instrument." As usual, Brune has a comprehensive knowledge of the subject, and could clearly distinguish between my error and the actual finish on the guitar, but he doesn't say how he could tell. RNJ
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