Streaky lustre from 1921 to 1926

[Peckris]

As promised ...

If it was a nice chocolate brown I'd be thinking, "wow, a bronzed proof!", but this is just peculiar.

[£400 for a Penny ?]

I wish you hadn't put that up, now I want one. I seem to want everything everyone shows

This is my take on it:

There are two types of copper oxide: copper (I) oxide and copper (II) oxide. Copper (I) oxide is referred to as cuprous oxide, while copper (II) oxide is known as cupric oxide.

I'm not a metalurgist, but my understanding is that type one (CU2O) is formed from exposure to air and moisture and produces the more often seen toning and taken to extreme's, verdigris, wheras type two (CUO) is blackish and can be caused by exposure to heat.

So, my vote is that this very nice penny you have here is oxidised with CUO.

Jumping in my time machine, I can see a peasants croft with smoke curling up into the night air from a log burning stove. Inside, 4 friends are playing cards, one spots this penny and thinks "ooh, a new penny, I must save that for little joe" and reaching out, he put's it to one side, on the stove.....

[VickySilver]

Those copper "oxide" states reflect levels of ionization and would reflect generically the state of the copper and not the specific salt such as chloride, sulfide, etc. It is the right general idea, however it is the oxidizing substance that determines the appearance of the surface of the coin with the chloride and chloride compounds giving the familiar green and usually the sulfides that give the "rainbow toning". The anion is not usually oxygen. I do not pretend to be an expert but the reactions can actually be quite complex and many times more than one type going on with respect to the surface of any one coin.

[Peckris]

Well thank you for the kind comments and the chemistry lessons! I do admit, it's a handsome piece. It was actually a greenish colour (not verdigris) when I first got it, and I can't remember what I did to remove the green, but that's the way it looks now.

"Coppered proof" anyone? Yours for £400...

[scott]

i have a 1937 penny that has sort of greened, not verdegris either.

what causes silver stuff to tone a golden colour

[Gary D]

I have a 1940 penny that tones a silvery colour, I wonder what would cause that?

Edited August 10, 2009 by Gary D

[£400 for a Penny ?]

I have a 1940 penny that tones a silvery colour, I wonder what would cause that?

Well, I guess again that it has oxidised in a certain way as to give off the silvery colour to which you refer. May be a result of the composition of the alloy, or it may have been in contact with something else which has 'contributed' to the reaction.

I suppose given it's 1940, it's not impossible that the mint were experimenting with composition/treatment - as you know, the next few issues get the 'Hypo' treatment.

Any chance of a pic ?