Questions About Toning

Beautiful rainbow toning is just an attractive form of very mild surface corrosion, and in that transitory state, can be unstable.
If you like this type of toning (as most collectors do), the coin has to be preserved in it's current state by complete isolation in an airtight capsule. Slabbing is not enough to achieve this most effective method of preservation.

Toning can and does happen on all coins,
but attractive toning is at it's best occurs on high grade silver and bronze coins.

Toning can have huge variation in it's presentation on coins, from highly attractive to downright ugly. Always, it is the differing prevailing environments and length of time which can produce this huge variations in toning.

Some of the best examples of highly attractive toning I have come across are, unfortunately, fake. In some of these cases, it can be very difficult to determine with 100% accuracy, if the the toning fake or not.
For this reason, I do not ascribe any extra value to a coin with nice toning, but I sometimes devalue the coin if the toning affects the grade.
In almost all of these cases the toning (or patination, or corrosion, or whatever you may call it), looks very un attractive anyway.

On the other hand, I will not devalue a coin in high grade, if it has attractive toning.

why are most toned 1973 mountie dollars toned golden? is it something in the metal? this cant be due to environmental factors.

I'm always a little suspicious of the clown-car toning. It looks dramatic but I wonder how much of it is the result of a specific chemical treatment? Not zero! It's a way to convert some relatively low-value coins into more sought after collectables.

Toning is caused by reaction of raw metal with Earth's atmosphere. It can therefore occur on any coin, mint state or otherwise. It tends to be more noticeable on mint state coins, because the dullness of circulation tends to hide the more subtle shades of toning.

The colours are caused by the thin film effect", the same optical phenomenon that causes colours to appear on oil slicks and soap bubbles. In the case of a coin, the "thin film" in question is a microscopically thin layer of oxidation and/or other corrosion byproducts. The colour depends on the thickness of the layer, witht he colours following the same pattern as the rainbow: red is thinnest, then orange, yellow, green and blue. After blue comes black, because at that point the "thin film" becomes too thick for light to pass through it.

"Fake toning", also known as "artificial toning", comes in two flavours. You've got "synthetic toning", generated by the application of chemicals that a coin isn't likely to find in nature. Chlorox bleach can generate some rather wild colours, for example. Then you've got "accelerated toning", where the chemicals used are identical tot he chemicals that cause natural toning - only the amount of chemical is greatly increased, causing the toning to appear in mere minutes or hours, rather than the years a natural tone can require.

How to tell the difference between natural, accelerated, and synthetic toning? Synthetic is perhaps the easiest to spot, as the colours tend to look "un-natural", You can also use chromatography to try to spot the telltale chemical residues of the toning agents, though not everybody has a gas chromatograph just sitting around their house. The TPGs, however, have access to chromatography gear and will use it on a coin they deem to have suspicious toning..

Accelerated toning is harder to spot, since the chemical processes that created it are essentially identical to "natural" toning.