THE BLUES - What causes this bright blue toning on copper?

[James_OldeTowne]

No, not the St. Louis Blues....

 

Check out the blue toning on these three foreign coins, especially the upper-right coin. These are just as they looked when I fished them out of a wooden box of foreign bulk coins:

 

obverse

reverse

 

We once sold a common Randall Hoard large cent with similar bright blue toning - and got a LARGE premium for it. The same customer recently bought another large cent from another dealer, and it was incredibly brilliant blue, like it was battery-powered. Also, three of the higher-grade coins in my Indian cent album have some blue highlights.

 

I like copper with this type of tone, and would appreciate any insight.

 

James

[truthteller]

Heat will turn copper blue or violet. Some of those gorgeous early proof indians were 'created'. Unlike artificial toning on silver, copper reacts more uniformly and quickly when heat is introduced. To attain a deep blue effect, heat must be slowly added to the coin and raised very high. Heating too fast will cause a splotchy effect. Take any mint state COPPER coin and try it, results will vary. No spot welders torches or bunsen burners and remember, no flame in contact with coin surface. Remember, this experiment is purely to recreate effects of heat and to know what to look for. The coin doctors' processes are much, much more sophisticated.

 

 

TRUTH

[gmarguli]

MS70 on dark copper will frequently turn them blue.

[jom]

OK, you Smarty Pants's, how come the Statue of Liberty turned GREEN?

 

jom

[chinook]

Because it's from France!!

[braddick]

MS70 on dark copper will frequently turn them blue.

Iodine with gentle heat has the same affect and allows the luster of the copper to still blaze through.

[Leothelion]

That does it! I'm getting my propane torch out! Lookout buyers, here I come!

 

Leo

[James_OldeTowne]

I doubt these coins would have been doctored, and they can't be worth much more than a dime each. They were just dumped in a wooden box along with a bunch of other junk, and had just been sitting there for years. If it's of any help, many of the other copper coins were slightly corroded, with that green growth you sometimes see, and some of the silver was just about blackened as well.

 

I tried the MS-70 trick on a couple of junk coins, and while they take on a slightly bluish tinge, it was more of a "flat" tone. The coins I linked are BRIGHT blue (in person), like the blue color is actually part of the luster.

 

Thanks for the thoughts. If anyone has any other "bright" ideas, I'd love to hear them!

 

James

[James_OldeTowne]

(bumped, because of being referenced in another thread)

 

The ebay coins in question are obviously long gone, and honestly, I don't particularly remember the coins that I was selling.

 

James