I have seen the word "Patina"

[Rhubarb]

Can anyone explain what it is? How it get's there? And where the word came from? Everyone uses it I just don't know what it is.


Rhubarb

[Robert]

My 1913 Webster's Revised Unabridged Dictionary defines it as:

1. "A dish or plate of metal or earthenware; a patella."

2. "The color or incrustation which age gives to works of art; especially the green rust which covers ancient bronzes, coins, and medals."

Etymology: "Italian, from Latin "patina" a dish, a pan, a kind of cake"


So it's a nice way of saying "oxide".

I guess that if it's an inexpensive coin, it has "toned". If it's an expensive coin, it has a "patina".

[Steven]

Try this.

http://www.google.com/search?gbv=2&hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=define:Patina&spell=1

[Rhubarb]

You can alway's rely on a google search. Thank's Steven

Patina: The change in an object's surface resulting from natural aging due to wear and oxidation. Antique jewelry is expected to have this patina and the value of the piece may decrease if it is cleaned off.

Rhubarb

[Dick]

The word "patina" is the name of the surface condition that is REMOVED by CLEANING!!!! The NATURAL oxidation, toning, etc that occurs when any metal is exposed to the air. Not technical, but plain english!
Dick

[Robert]

To explain how oxidation happens, you have to get into chemistry. Basically, oxidation is part of an "oxidation-reduction" reaction in which one substance becomes "oxidized" while another becomes "reduced". All that means is that electrons are traded among the components in the reaction.

For example, if you put copper in an environment where oxygen is present, it will begin to combine over time. The copper "oxidizes" or loses electrons to the oxygen. The oxygen is "reduced", or gains electrons from the copper. This shift in electrons, generally speaking, causes the copper and oxygen to bind together. This reaction takes a while to be visible with the naked eye, but heating the copper will make it happen faster.

It's more complicated than that though, because there are different "flavors" or valences of copper and they combine in different ratios with oxygen.

Example: One oxygen atom can combine with 2 copper (I) atoms to form cuprous oxide, a reddish powder. Or, that same oxygen atom can combine with only 1 copper (II) atom to form cupric oxide, a black powder. Confusing, huh?

The green patina seen on many copper roofs and the Statue of Liberty (yes, it was made out of copper/bronze) is the result of copper combining with (mostly) sulfur atoms from the atmosphere.

Not 100% sure, but I would think the "brown" color/toning of Lincolns comes from cuprous oxide.

If you're intertested, here is a link that tries to explain it all in a nushell.
http://en.wikipedia.org/wiki/Oxidation

[eagames]

The reason copper is used for things that people want to last such as they once used thin sheets of it to cover ship hulls or roofs and they used it for coins is:

When fresh copper oxidizes it grows patina very fast and the patina becomes a protective layer that stops corrosion that would ruin it. That's why copper things last so well.

When they galvanize other metals it's the same thing they put something on it that grows a protective oxide but copper does it by itself.

[Dick]

For those of you who are not familiar with "native copper", it is as the name implies, pure copper that occurs in AZ, among other places. I have seen it while working in the mining industry. It always is a very dark brown, almost black. Gold will also be found BLACK, due to the "varnish", covering it gets, over the years, when exposed to the elements, in the desert.
Dick

[Robert]

Ed, you're technically accurate about how fast copper reacts with oxygen. But it takes much longer to form the "patina" everyone's talking about. The instantaneous reaction covers a layer just a few atoms thick. That surface layer of oxides probably isn't detectable by the human eye. It takes longer for the copper unerneath that oxide coating to react. You need more than just the surface atoms to react if you want to see a patina.

The same can be said of aluminum. If you take a nail and make a foot-long scratch on it in one big motion, by the time you stop making the scratch, the aluminum that was scratched first has already completely reacted with oxygen. The full reaction is that quick. But again, it's only a few atoms thick so it still looks "fresh". Given time, it will slowly develop the chalky white look we recognize in old, weathered aluminum. That's aluminum oxide, Al2O3. The thicker that oxide layer, generally speaking, the better it is at "protecting" the underlying aluminum from additional corrosion. There comes a point at which the layer is so thick that it effectively stops the reaction... oxygen takes longer and longer to fight its way to the pure aluminum beneath the layer. A sort of stasis occurs and the aluminum might be considered to be meta-stable.

Alumina (aluminum oxide) is also very hard, so it's used as an abrasive. Powdered alumina can be ground so fine that it looks like flour and gives a truly mirror-like finish to metals.

[Robert]

Dick,
Did you happen to work for Phelps-Dodge? Or Kennecott up in Utah?

I didn't work for either, but I knew some people who worked for PD and I've seen some of the operations that go on at Kennecott. That mine is impressive!

[Robert]

Kennecott:

click here http://en.wikipedia.org/wiki/Kennecott_Copper_Mine

and then click on the photo on the right. If you look near the bottom of the pit, on the far side and on the near side, you'll see some strange dots on the road. Those are dump trucks. HUGE dump trucks.

Look at the stariwell in front of the radiator grille. http://www.cat.com/cda/layout?m=37840&x=7&location=drop

Dump truck specs: http://www.cat.com/cda/layout?m=37840&x=7&location=drop

[Rhubarb]

Kennecott, I work for a company called Southwire Co. When the Copper Division Southwire was open we would get the copper from Kennecott. Now we buy slabs from oversea's.



Rhubarb

[Dick]

Robert, I didn't work for Kennecot, but I did work for Baghdad Mining Corp, in AZ. Also for ASARCO, in Tucson. WE had some large trucks there, too. KW-Darts. The only thing small about them were the tires. Only 8' tall!. $9000. each, (in 1973). I have worked in the mines, off, and on since 1940. Add a war, a year on the AT&SF, as a Fireman, (Steam engines), then in Dec.,'57 back in the "bloomin naivy". LAter on I worked for KAiser Steel, in Fontana,CA. '83, to Mexico, and then back in '88. Then I was prospecting for about 14 years, before coming to CA.
Dick