Sir Sisu Posted September 21, 2005 Report Share Posted September 21, 2005 A couple of questions have been roaming my thoughts recently; one due to recent discussions here about toned and cleaned coins. The other is just from my own thoughts. I came to thinking that others might have similar one-line queries that they would like cleared up as well, so I thought why not place them all in one thread. Or perhaps you have heard a question repeated over and over again and would like to clear it up for others. Ask the question and then answer it yourself for the benefit of others. I think it would be great for new collectors. I think even experienced collectors could benefit from answers outside their own specialty. For those that answer, whenever possible, it would be great if you could provide either a link to a site supporting your answer or then perhaps a bibliographic reference to a published source instead. Of course this is not always possible, so please do not let that stop you from answering. The two thoughts that I have had can be put into simple statements:......... Link to comment Share on other sites More sharing options...
Sir Sisu Posted September 21, 2005 Author Report Share Posted September 21, 2005 Toning/tarnish actually provides a protective surface layer against deeper, more intrusive corrosion on a coin. Fact or Fiction? Link to comment Share on other sites More sharing options...
Sir Sisu Posted September 21, 2005 Author Report Share Posted September 21, 2005 BU status is normally given to those coins first struck with new dies. Fact or Fiction? Link to comment Share on other sites More sharing options...
ccg Posted September 21, 2005 Report Share Posted September 21, 2005 BU status is normally given to those coins first struck with new dies. Fact or Fiction? Fiction. I will call any coin "BU" provided that it is 1. Uncirculated 2. Has full lusture 3. Is not toned. Link to comment Share on other sites More sharing options...
Guest Stujoe Posted September 21, 2005 Report Share Posted September 21, 2005 BU status is normally given to those coins first struck with new dies. Fact or Fiction? <{POST_SNAPBACK}> I will quote the PCGS Lingo Guide and then make my own comments: "Brilliant Uncirculated A generic term applied to any coin that has not been in circulation. It often is applied to coins with little "brilliance" left, which properly should be described as simply Uncirculated." http://www.pcgs.com/lingo.chtml?universeid=313&letter=B BU, in my experience, is just a generic term for an uncirculated coin. In my opinion, it should be an untoned, uncirculated coin with brilliant luster but that is not the way it is normally used as far as I can tell. In the US it is often used for either sliders or Butt Ugly coins that would be MS60 at best. More of a marketing term or euphemism than anything else in actual practice. I think BU may be kind of a hold over from the old style if US grading that went BU, Select BU, Choice BU, Gem BU, etc. You will find that grading scale still in use sometimes today and the adjectives are supposed to correspond generally to numerical grades. Not sure on this, though, as that is all way before my time. Link to comment Share on other sites More sharing options...
Guest Stujoe Posted September 21, 2005 Report Share Posted September 21, 2005 Toning/tarnish actually provides a protective surface layer against deeper, more intrusive corrosion on a coin. Fact or Fiction? <{POST_SNAPBACK}> This I do not know. All I can tell you is that tarnish is caused by sulphur reacting with the silver. I guess it would be a more stable compound than the silver by itself but I don't know for sure. I think we need a chemist. Link to comment Share on other sites More sharing options...
Conder101 Posted September 22, 2005 Report Share Posted September 22, 2005 It varies. With some metals an oxide or sulfide layer will act as a protective layer and delay further "oxidation" On others the layers are not protective and further reaction will continue deeper and deeper into the surface of the metal. In extreme cases such as with iron the oxide layers will actually spall off of the surface constantly exposing fresh material to the corrosive effects. The patina on a copper coin is usually protective, that on a silver coin usually indifferent and the oxide layer that forms on aluminum is very protective. (Aluminum is actually very reactive and upon exposure to oxygen immediately forms a thin layer of aluminum oxide, one of the hardest substances known. The dense packing of the atoms in this oxide layer protects the surface below. A polished aluminum surface will often remain shiny for ages protected by that oxide layer. Link to comment Share on other sites More sharing options...
Ætheling Posted September 22, 2005 Report Share Posted September 22, 2005 Condor beat me too it, Al jumped straight out at me as being a casebook example of protective corrosion. Whereas Fe is your casebook example of destructive corrosion. Link to comment Share on other sites More sharing options...
jlueke Posted September 22, 2005 Report Share Posted September 22, 2005 But in all cases the product of the corrosion is more stable than the metal otherwise it would not be forming by themselves. Link to comment Share on other sites More sharing options...
Ætheling Posted September 22, 2005 Report Share Posted September 22, 2005 But in all cases the product of the corrosion is more stable than the metal otherwise it would not be forming by themselves. Generally speaking this is true. Although there are examples out there of reactions that create instable products naturally. Realgar for instance is a naturally occuring sulphide of Arsenic however it is instable in light and slowly breaks down into Pararealgar (Originally thought to be the closely related Orpiment). All three are Arsenic sulphides that form naturally. Link to comment Share on other sites More sharing options...
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