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I randomly came across a picture of this. It's the comparison between right handed and left handed people. As more people use the door handle, the metal becomes more faded and turns gold color. What is this gold color underneath and why does friction between your fingers and the door handle cause this reaction?

enter image description here

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    $\begingroup$ Consider using more particular titles, this one is too general, being rather a click bait. If you was a writer, you would not probably name your book "What is this story about ?". $\endgroup$
    – Poutnik
    Nov 11 '20 at 9:25
  • $\begingroup$ I have changed the title to be little more descriptive. Feel free to modify it if you udo not like it. $\endgroup$
    – Poutnik
    Nov 11 '20 at 12:19
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    $\begingroup$ @Poutnik I probably wouldn't even use "chemical reaction" to describe grinding a metal surface. The question is pretty much the same as to why the chopped water melon being green from outside has red-colored cuts. Not much chemistry to begin with, really. $\endgroup$
    – andselisk
    Nov 11 '20 at 13:38
  • $\begingroup$ @andselisk I fully agree with you. But I have intentionally formulated it rather from POV of the OP, wondering about chemical reactions, than from my POV, backup up by some knowledge or experience. $\endgroup$
    – Poutnik
    Nov 11 '20 at 14:11
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It looks like a brass ( a class of alloys, containing mostly copper and zinc, being golden-like ), which surface was covered by protective plating , possibly by chrome or nickel(*). It was probably worn out mechanically and/or by corrosion due acidic sweat.

(*)Nickel plating could be worn out easier than hard and resistant chrome.

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  • $\begingroup$ I understand nickel plate is more common on many decorative items today because of lower "shine" compared to chrome. $\endgroup$ Nov 11 '20 at 15:36
  • $\begingroup$ @blacksmith37 Could be. I am no specialist here. But I know Ni plating of Cu goes well by both galvanic and chemical way. I also remember watching Canadian documentary serie about airplane disasters, where in 1 episode the disaster cause was the worn out and snapped stainless steel string, because contained nickel caused faster mechanical wearing out than pilot expected. Routine controls require since than more frequent checks of stainless steel strings in small aircrafts. It was more corrosion resistent for maritime usage, but mechanically more vulnerable. $\endgroup$
    – Poutnik
    Nov 11 '20 at 15:50
  • $\begingroup$ I watch most similar documentaries ; all produced by people who do not know the technology. Aircraft cables are cold drawn stainless ( 301, 302, 304 ) so an affect of nickel makes no sense, The cables should be in a relatively dry corrosion free environment inside the aircraft. $\endgroup$ Nov 12 '20 at 15:03
  • $\begingroup$ @blacksmith37 That specific use was about a small pacific inter-island jumper, so corrosion was an issue, or at least that was reported as the reason why the usual material was not used. It was a naked string, not a cable, if cable means some isolation, which was moving along some guiders, what was mechanically wearing it out until the break. 301 has 6-8 % of Ni, 302 8-10%, 304 8-10.5% ( meadmetals.com/metal-products/stainless-steel/…). What do you mean by "So effect of nickel makes no sense ?" $\endgroup$
    – Poutnik
    Nov 12 '20 at 15:16
  • $\begingroup$ Maybe a language difference ; steels are not made as "strings" , steel comes a single wire, or multiple wires braded into cables. Aircraft use cables so they have redundancy, then even with a few individual wires broken the cable can still function. Nickel is homogeneously distributed in austenitic SS , so there can be no" failure of nickel". Cold worked 18-8 type stainless would be a poor choice of material for maritime corrosion. As I said ,the people that produce these shows do not understand the technology. $\endgroup$ Nov 12 '20 at 21:11

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