6 ms·

Understanding how silver objects tarnish

42 points by _Microft 5y ago

diimdeep 5y ago
Very interesting! Recently was thinking whether it is worth it to give a silver-plated cup as a present, and was skeptical because of silver tarnish over time. Not sure yet.
- kergonath 5y ago
  Silver tends to develop a patina, which can be much nicer than boring shiny silver. If the intent is to have a pristine, sparkling object, then sure, silver is not the right metal. However, I really like the aspect of properly maintained silver items. If the item is plated, the thickness of the coating is crucial. Polishing will remove some of the metal and over time the plating can wear off.
murbard2 5y ago
> People (intestinal gas emissions containing hydrogen sulfide) He who unleashed it tarnished it.
mikewarot 5y ago
Side note, sulfides are why hard boiled eggs turn green if you cook them too long.
- Etheryte 5y ago
  In case you missed it, this is explicitly brought up in a separate section in the article.
derbOac 5y ago
This explains a lot! My wife used to have this old silverware set, which was tarnished, and I was always complaining about how the pieces smelled like onions, especially if they were heated a little. She always made fun of me (she and my family think I have an uncanny sense of smell so they're used to it), but this makes sense to me now. My family always had stainless flatware so that was really the only set I was exposed to regular use of.
- murphyslab 5y ago
  The sulphide layer that develops is quite non-volatile, so that likely wasn't a direct source of the smell. It would likely be another organic compound and there is a known mechanism for iron. Compounds in our skin and sweat can react with the iron producing carbonyl- and organophosphine compounds. [0] Those compounds are more volatile than the original biomolecules and are quickly detected by our nose, possibly as an evolutionary response to blood. Similar processes would surely happen with other metal surfaces, and having a sulphide layer may even play a role providing reaction sites. [0]: https://phys.org/news/2006-10-iron.html https://phys.org/news/2006-10-iron.html
  - derbOac 5y ago
    Yeah after reading about it more I was wondering if maybe some other organic sulfide compound was reacting with it and creating the smell. I did never smell it on any other dishes or flatware, and it never went away with washing.
murphyslab 5y ago
During my masters thesis I worked in the lab of an electrochemist studying the adsorption of thiol(ate)s on precious metal surfaces. Organosulphur compounds have an incredible affinity for soft metal surfaces. His parents lived over in Calgary, Alberta, and he recounted to me several times how it was impossible to keep silver clean there due to the the occasional outgassing of oil wells north of the city. It was little enough that nobody's life was at risk, but high enough that true silverware would reliably be tarnished within a month or two.
- xyzzy21 5y ago
  This is why "polishing the silver" was a routine and repeated task for servants from the 19th century back. Imagine how much silver was last and discarded by doing this!
d_silin 5y ago
Pure silver (99.99%) can be restored to pristine color by heating to 500C until silver sulfide decomposes. Doesn't work with sterling silver, as copper sulfides oxidize to stable copper oxide (which is black as well).
deleted 5y ago
[deleted]
nlh 5y ago
Among coin collectors, we call the process “toning” instead of tarnishing (a much more benign word, IMHO ;) It’s the exact same chemical process, most commonly seen in old silver dollars that were stored in sulpher-containing mint/bank bags. Just the right amount of toning can turn a silver-colored silver coin into a rather magnificent rainbow that can be worth many many times the value of the exact same coin without the coloring. Exhibit A: Regular silver dollar (still quite beautiful!) https://images.pcgs.com/CoinFacts/25003275_37921476_2200.jpg https://images.pcgs.com/CoinFacts/25003275_37921476_2200.jpg Exhibit B: Rainbow toned silver dollar that can be anywhere from 3-100x the price of a non-toned coin: https://images.pcgs.com/CoinFacts/35923065_149932537_2200.jpg https://images.pcgs.com/CoinFacts/35923065_149932537_2200.jp... As one would expect, values like this have created quite the cottage industry of artificially-toned coins which can be anywhere from trivial to impossible to differentiate from naturally-toned coins. It can be somewhat of a cat and mouse game to detect :)
- azepoi 5y ago
  Patina should work too, can be used as a verb in french, se patiner, just patine as a noun.
carterschonwald 5y ago
I recently dabbled in small scale silver smithing last spring, and there’s 1-2 sterling silver alloys that have been commercially available in recent years are way less susceptible to tarnish. They replace some of the copper with two percent germanium (alloy trade name is Argentium ) and this sterling silver alloy gets a bright white color from heat treatment based passivation that also is a precipitation hardening process. It Does change some of the processing you do though; no need to pickle between steps, and this alloy is incredibly brittle and fragile while red hot (think like stale wet cake )! Interestingly, this sort of weak when red hot phenomenon is common for some bronze alloys too (and is part of why bronze stuff is more often cast or cold worked) Also has a way wider melting temp range which combined with being only 1/2 as thermally conductive as usual silver and copper alloys! This means the ways you sometimes work it heating wise feel more like what you’re working with a strange soft steel.
xyzzy21 5y ago
Fundamental fact of corrosion: it's 100% "battery" electrochemistry; without exception. That "battery" can be enhance by chemicals in the environment e.g. rust on cars from salt on roads or it happens naturally as the "device" was manufactured (e.g. dissimilar metals in plumbing such as copper and galvanized steel piping).

42 points by _Microft 5y ago

Very interesting! Recently was thinking whether it is worth it to give a silver-plated cup as a present, and was skeptical because of silver tarnish over time. Not sure yet.

kergonath 5y ago
Silver tends to develop a patina, which can be much nicer than boring shiny silver. If the intent is to have a pristine, sparkling object, then sure, silver is not the right metal. However, I really like the aspect of properly maintained silver items. If the item is plated, the thickness of the coating is crucial. Polishing will remove some of the metal and over time the plating can wear off.

murbard2 5y ago

> People (intestinal gas emissions containing hydrogen sulfide) He who unleashed it tarnished it.

mikewarot 5y ago

Side note, sulfides are why hard boiled eggs turn green if you cook them too long.

Etheryte 5y ago
In case you missed it, this is explicitly brought up in a separate section in the article.

derbOac 5y ago

This explains a lot! My wife used to have this old silverware set, which was tarnished, and I was always complaining about how the pieces smelled like onions, especially if they were heated a little. She always made fun of me (she and my family think I have an uncanny sense of smell so they're used to it), but this makes sense to me now. My family always had stainless flatware so that was really the only set I was exposed to regular use of.

murphyslab 5y ago
The sulphide layer that develops is quite non-volatile, so that likely wasn't a direct source of the smell. It would likely be another organic compound and there is a known mechanism for iron. Compounds in our skin and sweat can react with the iron producing carbonyl- and organophosphine compounds. [0] Those compounds are more volatile than the original biomolecules and are quickly detected by our nose, possibly as an evolutionary response to blood. Similar processes would surely happen with other metal surfaces, and having a sulphide layer may even play a role providing reaction sites. [0]: https://phys.org/news/2006-10-iron.html https://phys.org/news/2006-10-iron.html
- derbOac 5y ago
  Yeah after reading about it more I was wondering if maybe some other organic sulfide compound was reacting with it and creating the smell. I did never smell it on any other dishes or flatware, and it never went away with washing.

murphyslab 5y ago

During my masters thesis I worked in the lab of an electrochemist studying the adsorption of thiol(ate)s on precious metal surfaces. Organosulphur compounds have an incredible affinity for soft metal surfaces. His parents lived over in Calgary, Alberta, and he recounted to me several times how it was impossible to keep silver clean there due to the the occasional outgassing of oil wells north of the city. It was little enough that nobody's life was at risk, but high enough that true silverware would reliably be tarnished within a month or two.

xyzzy21 5y ago
This is why "polishing the silver" was a routine and repeated task for servants from the 19th century back. Imagine how much silver was last and discarded by doing this!

d_silin 5y ago

Pure silver (99.99%) can be restored to pristine color by heating to 500C until silver sulfide decomposes. Doesn't work with sterling silver, as copper sulfides oxidize to stable copper oxide (which is black as well).

deleted 5y ago

[deleted]

nlh 5y ago

Among coin collectors, we call the process “toning” instead of tarnishing (a much more benign word, IMHO ;) It’s the exact same chemical process, most commonly seen in old silver dollars that were stored in sulpher-containing mint/bank bags. Just the right amount of toning can turn a silver-colored silver coin into a rather magnificent rainbow that can be worth many many times the value of the exact same coin without the coloring. Exhibit A: Regular silver dollar (still quite beautiful!) https://images.pcgs.com/CoinFacts/25003275_37921476_2200.jpg https://images.pcgs.com/CoinFacts/25003275_37921476_2200.jpg Exhibit B: Rainbow toned silver dollar that can be anywhere from 3-100x the price of a non-toned coin: https://images.pcgs.com/CoinFacts/35923065_149932537_2200.jpg https://images.pcgs.com/CoinFacts/35923065_149932537_2200.jp... As one would expect, values like this have created quite the cottage industry of artificially-toned coins which can be anywhere from trivial to impossible to differentiate from naturally-toned coins. It can be somewhat of a cat and mouse game to detect :)

azepoi 5y ago
Patina should work too, can be used as a verb in french, se patiner, just patine as a noun.

carterschonwald 5y ago

I recently dabbled in small scale silver smithing last spring, and there’s 1-2 sterling silver alloys that have been commercially available in recent years are way less susceptible to tarnish. They replace some of the copper with two percent germanium (alloy trade name is Argentium ) and this sterling silver alloy gets a bright white color from heat treatment based passivation that also is a precipitation hardening process. It Does change some of the processing you do though; no need to pickle between steps, and this alloy is incredibly brittle and fragile while red hot (think like stale wet cake )! Interestingly, this sort of weak when red hot phenomenon is common for some bronze alloys too (and is part of why bronze stuff is more often cast or cold worked) Also has a way wider melting temp range which combined with being only 1/2 as thermally conductive as usual silver and copper alloys! This means the ways you sometimes work it heating wise feel more like what you’re working with a strange soft steel.

xyzzy21 5y ago

Fundamental fact of corrosion: it's 100% "battery" electrochemistry; without exception. That "battery" can be enhance by chemicals in the environment e.g. rust on cars from salt on roads or it happens naturally as the "device" was manufactured (e.g. dissimilar metals in plumbing such as copper and galvanized steel piping).