 The Clarinet BBoard
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Author: skygardener
Date: 2006-11-22 10:23
Hi,
I read on the keepers page Mr. Behn's ideas about patina, but there are a few specifics that I am unsure of.
He said that some mouthpieces having excessive patina will have a very weak surface layer, and also that certain things like moister and sunlight can accelerate the progression of the patina.
But my questions:
1. Is the patina really connected to the weak surface layer? I.e.- Can an old mouthpiece have no patina, but still have a weaker surface that scrapes off?
And on the other side of the coin:
2. If one were to quickly and purposely induce a patina on a new mouthpiece would it be come weak?
Finally (possibly the same questions as above in a different phrasing),
3. Does hard rubber “age” inside and out, too? As we all know rubber bands change and become weak very quickly, and even some plastics become brittle in only a few years. Is there a difference between the hardness or softness of any given formula of rubber today and the hardness it will be in 50 years?? Have there been any tests of this?
Thanks all,
Sky
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Author: Terry Stibal
Date: 2006-11-22 15:20
Plastics (in the strictest, 1800's sense of the word) all have two basic components. One is the "resin", the body that makes the object hard once the plastic has set. The others is the "plasticizer", a 'solvent' that has to be used to make the "resin" moldable but then needs to go away to make it "set".
Some "plasticizers" are pretty simple - good old organic camphor (from the plant of the same name) used to be used with early plastics like camphorene. Others are more complex - rubber (a plastic within the true meaning of the term) uses a variety of compounds to enable the molding of the rubber itself. And some, like the phenolic resins and epoxies, are very complicated indeed.
One thing that most plastics share to some extent is that the composition of the plastic changes over time. True, some are very stable (poly-carbonate (Lexan, for one), but others will just up and change on their own, given enough time or exposure to environmental chemicals.
To take one example, polystyrene, it behaves both favorably and unfavorably through this behavior. Given enough time, styrene (the "resin" in the polystyrene) will actually harden up from a near liquid to a solid. This ease of conversion from a fluid to a solid is one reason why we see so much of it used.
However, it works the other ways as well. Those raised with plastic modeling know of old model kits that, without any obvious external cause, turn brittle, change color, and literally fall apart into fragments or dust. This is due to the reaction between the remaining plasticizer in the molding with the atmosphere and light; as the residual amounts draw down the plastic becomes less so over time and ultimately fails from its own weight.
Rubber is special, but it still shares these problems. Natural rubber is a wonderful substance, capable of coherent elongation way beyond any other natural substance known to man. However, the long molecules that enable this behavior have their own problems in other areas. Placed outside of its natural "comfort range", untreated natural rubber either becomes extremely brittle (at lower temperatures) or a gummy, sticky mess (at elevated temperatures). So, while it had some wonderful qualities, it was largely useless due to these defects.
Charles Goodyear's only useful contribution to the world (the guy was a major league failure in all other areas of his life) was that he mixed (note the word) sulphur with natural rubber, then placed the resultant "compound" under considerable heat to set the material in the shape desired. True, he only did it by accident, and true it took him many years to blunder into the solution. But, find it he did and the world (if not Mr. Goodyear, who died as he lived, a pauper, while others grew rich from his discovery) are a better place for it.
This "mixture" of natural rubber, carbon black, solid filler and sulphur made the rubber practical enough to produce moldable items, and the rubber industry literally exploded during the period 1850-1900. The use of rubber for just about every purpose on earth during that time enabled the beginnings of the modern plastic industry. Spend any amount of time in a museum dedicated to everyday life during that period and you'll see hundreds of items made from rubber, from combs to clothing, from toothbrushes to personal hygiene aids.
In order to achieve this "mixture" that works so well, rubber is basically "chewed up" and then "kneaded" with the fillers so as to distribute them throughout the mixture. (Early rubber items seen in section under a microscope resemble samurai sword blades, with hundreds of fine layers, all mashed together.) This "milling" process involved a lot of force in massive, nasty, man-maiming machines with large metal rollers, and in some form or another, it is present in all rubber production.
With the right fillers, rubber is amiable to a wide variety of uses. For example, take raw rubber, add some reenforcement fiber, a lot of carbon black, some stearate "soaps" and you get material that is useful for rubber tires. Jack in a healthy dollop of powdered lead with a few other fillers and you get ebonite, ready for clarinet production. Neat stuff.
However, like all other plastics, rubber is susceptible to age and environmental effects. All tires produced are dated, because it is a given that older tires, even if never used for driving, will eventually deteriorate to the point that they will no longer be safe. Atmospheric ozone and ultraviolet light combine to create this effect. And, the sulphur that's mixed into the rubber (it doesn't really chemically combine with the rubber) will, over time migrate to the surface, degrading the rubber mixture in the process.
It's a slow process under most conditions, and it can be made slower by a few precautions. Covering up tires on seldom used vehicles (like the RV parked in your neighbor's yard) will retard the process considerable. But, sooner or later, all rubber stuff is going to reach the point where it's no longer "rubbery" (for the want of a better term).
Clarinets made of ebonite, and mouthpieces made of rubber stock also share this problem. That 'patina' that you see is actually the outer layer of the mixture, where sulphur and other substances have started miagrating from the item. That I've seen older (1880's) ebonite horns that have cracked, usually at a post insertion point. And, my favorite clarinet mouthpiece (a Selmer HS* from God knows when in the past) has a uniform yellow-green coating over its exterior that is (according to my friends in the rubber industry) the sulphur "leaking" out of the mouthpiece.
Initially, this is not harmful (or so the rubber guys say). However, as more and more of the sulphur leaves the mix, the dimensions of the mouthpiece will become less and less stable (since the rubber remaining is now free to "flex"). ULtimately, enough will leave that the mouthpiece may fail or become too flexible, either to hold a good chamber shape or to hold proper rails and tip dimensions.
The only solution is to scrap the item and start over. The easiest solution proposed by the "rubber men" was to have a new casting made. That not being practical, the next-best solution is to have a copy made to the same dimensions. I had this done back in the 1980's, and I use the two mouthpieces interchangeably to this day.
Incidentally, there is a "rubber reclaiming" industry, which reverse vulcanizes rubber to remove the sulphur (the item that "locks" the finished item in it desired form. The rubber is cooked in high pressure autoclaves, and steam and other substances "melts" the sulphur out of the mixture. The result, while not as good as virgin rubber, still serves quite well for many purposes.
An excellent book that covers this in much greater detail is called Plastics. Written for the lay person, the author (a business writer) traces the history and chemistry of all plastic compounds, from celluloid and Bakelite and rubber through the ones so common today.
leader of Houston's Sounds Of The South Dance Orchestra
info@sotsdo.com
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Author: Bob Phillips
Date: 2006-11-22 16:31
When I was a kid making model airplanes, we used to "plasticize" the dope (the highly volatile "paint" used to shrink and seal the paper covering) with small amounts of castor oil. The material was a resin, a solvent -that evaporated after application --and the optional plasticizer.
Thus, I've always thought of a plasticizer as a small quantity of added "oily" substance that kept the resin from becoming brittle with age.
Terry Stiebel's explanation of rubber compounding and aging makes me wonder if my understanding is erroneous.
Bob Phillips
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Author: L. Omar Henderson
Date: 2006-11-22 18:11
Excellent post Terry.
The process of vulcaniztion is cross-linking the long monomer stands. Early vulcanization processes were hampered by sub-optimal catalysts - primarily sulphur and raw materials tainted with contaniments e.g. plant protein, metals, etc. that modified the cross-linking patterns. The quality of raw rubber resin improved dramatically within the last 20 years because of the need for a higher quality starting material for latex gloves. Older rubber plantations have given way to more modern rubber farming techniques. The older machinery used, variable timing and temperature regimes, all contributed to variable end products in the chronology of vulcanized rubber manufacture. Tempering, heating cycles also helped produce a better product. Many of the manufacturing and tempering details of manufacture of older rubber mouthpieces have been lost or really not reproducable with todays machinery and raw materials but with modern technology the cross-linking signatures of old vulcanized rubber can be determined and perhaps close approximations of these signatures (but not the original) can be duplicated. We can only duplicate the rubber in its condition today - certain conditions of trace materials also cannot be duplicated. Do we know if this actually makes a difference in sound qualities??? - your guess is as good a mine !!!
Vulcanized rubber will begin to degrade - breaking cross-links - immediately after manufacture. This process to degradation may take many years but is accelerated by environmental conditions such as UV radiation, oxygen and ozone, and air pollution. The surface of course is more prone to degradation and various batches of rubber-mouthpieces may react differently based on the amount of vulcanization and presence of excess sulfur (the earliest catalyst used) which migrate to the surface and form colored sulfur compounds which many refer to a patina. These sulfur compounds are very stable chemically and actually help reduce further surface degradation and migration of catalyst to the surface.
L. Omar Henderson
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