Take a close look at the four coins above.

Which of the four would you guess are artificially toned and which are naturally toned?

The answer? All four were cleanly graded as having natural toning by PCGS. Despite the kaleidoscopic colors, none of these Morgan dollars are considered artificially toned. But how can a collector understand the difference between vibrantly toned stunners like the coins above, all worth a hefty premium because of their toning, and an artificially toned problem coin worth no more than silver melt value? This article will explain the primary visual differences between naturally and artificially toned coins, allowing any coin collector to confidently and safely buy toned coins.

For those unfamiliar with the term, toning is a catchall word used to describe the coloration resulting from various chemical reactions that take place on the surface of a coin. Toned coins can range the spectrum—from jet-black to a multicolored rainbow. In the marketplace, attractively toned coins can demand substantial premiums and often sell for two times, three times...even as much as ten times the price of a equivalent untoned coin.

But one major problem within the toned coin market is determining the origin of the toning itself. Toning is not always the result of natural chemical processes. There are various techniques that can be used to artificially induce coloration. These methods are frowned upon by serious collectors, and artificially toned coins are viewed in the same negative light as cleaned, or polished coins. All of the reputable coin-grading companies refuse to grade artificially toned coins, instead assigning those coins a 'details' or 'net' grade. But it is not always easy to tell the difference between naturally (NT) and artificially toned (AT) coins, even for experienced collectors. In this article, I'm going to discuss a few ways to tell the two apart.

First off, it's important to clarify the differences between toned coins of different metals. Silver is the most chemically reactive noble metal, and often reacts with sulfur to form multicolored "rainbow" toning. Copper is even more reactive. The most typical form of toning for copper coins is a gradual darkening over time, from red mint luster to a brown patina. The vast majority of pre-20th century copper or bronze (copper-tin alloy) coins have a natural dark brown color. Those that have red mint luster have most likely been either dipped or otherwise restored, or coated in shellac or lacquer by early collectors. Coins with their original red mint luster get an "RD" designation added to their grade and demand premiums over brown or red-brown coins ("BN", "RB"). Multicolored toning is possible with copper coins, particularly U.S. Lincoln cents, but is slightly more likely to be artificial on modern coins. Nickel, or copper-nickel, coins are the least prone to toning. Attractively toned examples of nickel/copper-nickel coins should always be viewed with a certain level of skepticism, though it's still quite possible for the toning to be natural, particularly for proof Jefferson nickels (see Robec's Images Gallery for some great examples). A large portion of natural nickel toning is the result of environmental exposure or extreme conditions. That makes nickel coins especially prone to artificial toning methods that recreate those environmental conditions. Gold coins also have some potential for toning (most often red or purple colors) but are much less reactive than either copper or silver coins.

Artificially Toned Coins

Setting aside the toning propensity of different metals, the coloration itself will almost always help you determine whether you're looking at an NT or AT coin. Most artificially-toned coins have extreme coloration - the motto of the coin doctors seems to be "Go big or go home." A deep blue or purple surface, especially when coupled with abrupt color transitions, is an extremely strong indicator of artificial toning. Take a look at the 1991 American Silver Eagle coin on the right. ASE's are almost pure silver, so dramatic toning is not uncommon. But in this case, the coin has an unnatural deep aquamarine color as well as a very incongruous patch of violet/orange in the center of the obverse. That sudden contrast of colors is a telltale sign of rapid toning, which is almost always artificially induced.

Here's another example. This is a Morgan dollar sold by a high-volume eBay seller - he cooks these coins up to induce ugly "oil-spill"-style rainbow toning, then sells them for a premium. Notice the angular color swatches, and the abrupt transitions between colors. The colors are almost neon—this silver coin looks like something right out of a psychedelic trip. Stay far away from coins that look like these two, or else you risk overpaying for a junk coin worth no more than bullion value.

Naturally Toned Coins

Now compare those two coins to the beautifully-toned Morgan dollar on the right. The toning is still dramatic, but in this case the colors are much more of an evenly-balanced pastel—not neon—palette. There are no abrupt color transitions; the toning gradually blends from color to color- yellow to gold, gold to red, with a hint of purple and blue on the peripheries.

A couple times now I've seen this question asked by beginning collectors - "If the coin is only toned on one side, doesn't that mean it's not natural?" The short answer to that is no. While environmental factors are responsible for natural toning, it is quite possible for the obverse of a coin to be exposed to different factors than the reverse, or vice versa. Take the Morgan dollar, for example. Despite its massive popularity with modern collectors, the Morgan dollar was not a very popular coin while it was being minted. The dollar coins were large and unwieldly, and most people found paper money much more convenient to use. But because of the lobbying efforts of powerful silver mining interests in Nevada and other western states, the U.S. Mint still produced millions of the coins every year. A huge number of Morgan dollars never even saw circulation, but were instead held in bank vaults for decades on end. Within the bank vaults, the coins were held in burlap sacks, sacks that had been treated with a sulfur-based dye. Those conditions were extremely conducive to toning, but not all coins held in the bags toned. Toning only occurred on the surfaces of coins that were directly in contact with the sulfur-coated fabric. That's why so many Morgan have vibrant toning on one side, and absolutely no toning on the other side. Many Morgans also show crescent toning, where another coin sat between the Morgan and the bag, leaving only a small portion of the first Morgan in contact with the bag.

While this was by no means a comprehensive write-up, it should hopefully provide collectors with at least a couple of helpful tips for avoiding AT coins. We'll be addressing some further aspects of the NT/AT split in future articles, including the subtle distinction between naturally-toned and "market acceptable" coins.

More great articles on toning:

Monster Rainbow Toned Morgan Dollars - Jhon E. Cash (quite possibly the most comprehensive information resource on the web on toned Morgans)

Coin Toning - Reid Gold Coins Guide

Fake Rainbow Toned Coins - CoinTalk Forum Thread

Signs of Artificial Toning on Coins - Gainesville Coins