 The Clarinet BBoard
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Author: Bradley
Date: 2003-10-28 02:24
Just recently I asked the question about what keys were made of.
I was wondering if anyone knew what it is in our sweat* that helps eat away at the finish on our keys. I know it is the acid etc. that is harmful, but I was hoping someone could elaborate on what chemicals are present in particular and how they affect keys.
Thanks for your time.
Bradley
* sweat being defined as any substance our fingers leave behind on the keywork
Post Edited (2003-10-28 02:26)
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Author: GBK
Date: 2003-10-28 03:13
Caveat: As I opted not to sweat in High School, I did not take Chemistry, but rather, took Advanced Music Theory.
I believe sweat is comprised of sodium, chloride, potassium and water, although there may be some traces of fatty acids and possibly some protein.
I'm sure the Doctor, or JMcAulay will have a much more detailed analysis which will include the effects on keys, etc... GBK (no sweat!!)
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Author: JMcAulay
Date: 2003-10-28 08:56
What a good question! And GBK is off to a roaring start for a reply. Unfortunately, my response won't be as nitty-gritty as you would no doubt want. But perhaps someone else has knowledge unknown to me.
Human sweat is important to homeostasis, the body's tendency to maintain itself in status quo. One obvious aspect of this is liquid secretion for temperature maintenance. When the body becomes too warm, sweat is produced more profusely, thus increasing evaporation from the skin surface, which in turn reduces skin temperature.
Furthermore, sweat assists in maintaining the body's electrolyte balance, with secretions including a chemistry that varies depending on the blood serum chemistry. Hence, identifying the chemical makeup of sweat can't be done in an absolute sense, because many constituents change from time to time.
In addition, some proteins and peptides in sweat have antibiotic properties, so that sweat also helps to prevent rampant growth of skin bacteria.
And, by the way, some of this has been known only within the last few years.
Silver is not a highly corrosion-resistant metal as are, for example, gold and rhodium. Even mild acids will cause oxidation of silver (Pineapple juice is an excellent safe slow-rate oxidizer for decorative effects on tooled silver), and sulfur compounds in contact with silver may form silver sulfide. These and many other things can damage the appearance of silver.
Sebum, another skin secretion, is the primary source of fatty acids on the skin. And sebum is even more variable than sweat with regard to secretion rate and composition. This determines in part why some people have "dry" skin while others have "oily" skin. Age and sex are factors, as are to some extent diet and even serum cholesterol levels.
It is rather obvious that some people's skin secretions will react with silver rapidly. The skin secretions of some others have very little effect on silver. Many people can wear sterling rings (92.5% silver), for example, and the rings will retain a nice shiny appearance. However, some people wearing such rings will notice the ring becoming dark or developing unusual-looking colors. I do not know of any definitive study ever done to determine the exact cause(s) of these extreme differences, and I suspect that meaningful performance of such a study would be terribly difficult because of the great number of variables. Thus, any "information" related to this topic is likely based on guesswork, unless I have missed some amazing work that's been done.
Adding to the mystery is a considerable amount of anecdotasl information related to the disappearing of rhodium plating from "white gold" rings worn by some people. It's hard to understand how this might be caused by some chemical activity, as rhodium is extremely resistant to corrosion. It's also hard to understand how the surface of a ring could receive abrasion to the extent that rhodium, a very hard metal, goes away in normal wear for some people -- but not for others.
On the other hand, if you wondered about nickel or "German silver" (nickel silver) keys, that's a different situation. These, by the way, are easily polished with "Brasso," which is not recommended for silver alloys (nickel silver contains no silver). If you use it, I suggest: 1) remove the keys before polishing, and 2) be careful to keep the Brasso away from pads and axle bearing surfaces.
Regards,
John
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Author: Gordon (NZ)
Date: 2003-10-28 10:12
Porosity of the plating must also be a factor for corrosion.
Seeing there are strong electrolytes in sweat, if the sweat came in contact with both the plating and the base metal, then corrosion would occur, particularly pitting of the base metal.
This is galvanic corrosion. The sweat would act like sea water.
See: http://www.coastalfasteners.co.nz/galvanic_corrosion.htm
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