Silver plated copper

This just in! When the surface of a copper wire oxidizes over time the thin oxidation layer seals and protects the rest of the copper wire from further oxidation. Thus, while the effective diameter of the wire is reduced a hair, therefore resistance is increased a shade, oxidation doesn’t appear to be a real issue. 

geoffkait you are correct.A coating of oxidation does protect the rest of the wire.But the ends need to be sealed with something or they will degrade and not pass the signal properly.The good news is that it takes a very very long time to get to that point.

That’s what Deoxit and similar products are for as well as contact enhancers like the graphene paste. No big deal. Audiophiles are pretty well versed in electrical contact housekeeping protocols.

Just to clarify for everyone on this post - Copper oxidizes very rapidly but Silver does not.

A clean Copper surface prepared in vacuum forms a monolayer of Copper Oxide within minutes of exposure to air. A clean Silver surface prepared in vacuum forms a fraction of a monolayer of Silver Sulfide within minutes of exposure to air but no oxide within that timeframe. The tarnish observed on Silver is primarily Silver Sulfide.

I can mention the fact when a conductor silver, silver plate or copper is connected to a terminal of any sort..  IF the junction is sealed, the wire will not tarnish. If the junction is  somewhat protected from the air, (like in a plug but not sealed, it will tarnish slightly and take much longer to do so. If the connection is in 'open air' it will tarnish rapidly.Plus if you touched/rubbed bare copper strands with your bare hands, (like to twist the strands tight, etc)  it will tarnish even faster. 
And yes using a product like Caig Gold will lessen oxidation.  
For example, the silver plated wire inside AC plugs even after five years of use, had not tarnished. But the Same wire used for Magnepan 3.6 in the through hole back of the speaker, was very tarnished black in less than two years. (I am assuming the speaker vibrating was moving air back and forth through the open hole of the connector.