how do you tone coins ex. rainbow colors?

Answer 1

Artificial toning is probably one of the best ways to destroy the value of your coins. It typically results in intense colors of purple, blue, or red, and coin grading services will typically refuse to grade a coin they suspect has been artificially toned. In my opinion, most of the rainbow toned coins that are on the market that are ungraded (unslabbed) are phony and worthless.

See this commentary:
http://www.coingrading.com/ynotgrade1.html

Natural toning is the result of chemical reactions with the silver, copper, or other metal in the coin. Most attractive silver toning is the result of sulfur, while most black silver toning is from chlorides. Often moisture combined with paper rolls, or cloth mint bags will produce attractive toning. Sulfur was used in older mint bags as a preservative and would react with silver oxide on the coins to form a colorful patina. Paper used in coin rolls and small envelopes often contains sulfur also and causes toning. Another common source of toning were the old style coin albums, where round holes in cardboard held the coins. Different brands of coin albums even resulted in different types of toning as a result of different paper and ink compositions.

All that said, if you really want to find out how to tone coins there is nothing like experimentation.
1. Apparently bleach (chlorides) will turn your coins purple.
2. I think dipping in very dilute sulfuric acid is likely to give silver coins a yellow tone.
Whatever you try, I suggest you do it on worthless coins, because after you are done they are most likely going to have no collectible value.

Also see:
http://rg.ancients.info/guide/toning.html

Answer 2

There are both natural and artificial processes. Of course the natural processes involve a lot of aging. The reference is a good introduction to coin toning. (I never heard of toning before. Thanks for bringing the subject up!)

Answer 3

i might want to upload black, it contrasts properly with any of the present rainbow hues, and also to our eyes, both infrared and ultraviolet seem black, so black might want to be organic on both area of pink or violet.