Naturally or artificially by the reaction of the coin metal with the atmosphere, or any substance (paper, cardboard, felt, etc.) it comes in contact with, and it can be affected by the conditions of heat and humidity to which it is subjected, among other things. Remember, toning is a euphemism for tarnish, the darkening and/or corrosion of metal. The principal coin metals that tarnish or "tone" are silver, copper, and bronze alloys. Aluminum and zinc just corrode, iron/steel rust, and gold of the purity used for most coins is more or less immune. It depends. Ugly tarnish, at best, has no effect on price, and at worst can devalue a coin substantially. What many people (not including yours truly) call "monster toning" can add value to U.S. coins and some world coins. Even "toning" lovers generally agree that artificial toning is bad, but there are many issues involved in determining what is artificial and what is natural. BTW, you will probably get some answers disagreeing with my take on this subject, but that's OK, my feelings are tough to hurt.
im not too fond of the eratic rainbow toning.. to me thats ugly... but i do like the golden tones on the war nickels I believe it was you GD that showed those on another thread... very beautiful... Mach
Around 1970 I bought all kinds of gold 20 Francs ( Belgian, French, Suisse ) Sovereigns and 10 Florins from a bank on a regular basis and put them in a bankvault Around 1970 there was still a 25% numismatic value on old Sovereigns and other old coins When I wanted to sell the coins around 1980 they were suddenly all jewellers coins, cleaned, shiny etc and the same bank offered 5% below melt to have them melted ; the premium was gone too I showed them the purchase slips and they compromised ; they would buy back five coins and they never wanted to see me again Now I am a chemical engineer and took the challenge ; they wanted dirty coins : they would get dirty coins So I put all the coins on a high place above my french fry oilkettle I turned the coins weekly After three months of dayly french fries the condensed fats ( I used solid fat in my kettle ) had made the coins real sticky I then collected dust from my ten year old wine bottles and saturated the fat with dust until the coins were dry and not sticky I was then able to sell the coins for normal value to the bunch of guys that tried to defraude me in the first place The coins looked really icky and 100 year old , no minting lustre left But that was what the bank wanted dirty old coins
Notice I am from Belgium If you want a specific gold coin any bank can get a coin on the list of readily recognized coins at about 7% over spot (you order it ) Attached is the link to the exchange agent that provides some banks and the coins that are recognised http://www.eurogold.be/UK/main.htm However if you only want just a gold coin you can walk into any monyexchange agent making his living from changing dollars and yen and buying and selling goldcoins on the side He will be content with 2% over spot on what he has in his safe that day You hand over money and walk out with your coin
In the States just about all money changers, including those banks that do provide the service, deal strictly in bills and notes, and they neither accept nor provide coins.
That is true in Belgium too No foreign coins accepted or provided But goldcoins and goldbars are traded by virtually all exchange agents I suppose this has historical background
