To tarnish copper coins for further enhancement of their designs, I use the simplest sulfur-containing compound which is normally used by professionals to give the copper coins a gold-like brown patina. That technique requires a more delicate approach and perfect timing (all coin patinating methods are described here) which I am not going to bother with to accomplish a simple task here.

To prepare the required compound, I dissolve 20 grams of Copper Sulphate 5-hydrate (CuSO4·5H2O) and 5 grams of Potassium Permanganate (KMnO4) in 1 liter of water of the room's temperature.

In this method, the amounts of Copper Sulphate and Potassium Permanganate do not have to be exact. However, I should mention this: the larger the amount of Copper Sulphate in the compound, the more red the coins turn in color.

And if there is more than 5 grams of Potassium Permanganate in the compound, the coins will turn from dark-blue to black-violet in color.

One can tarnish coins by various methods, one of which is Sulfur/Vaseline Paste Treatment: the coin is covered with a thin film of the sulfur/Vaseline paste and kept this way until the desired tarnish is achieved. However, after undergoing this treatment, the coin's features would be hard to enhance. Only using the soluble sulphur compound with another substance can provide such an opportunity.

Now pour the soluble compound into an enameled bowl.

Preparing Patinating Solution

And heat it up to the boiling point. As soon as it boils, lower the gas flames and keep the compound boiling during the entire process. If you do it indoors, keep the kitchen (room, garage) well ventilated.

Heating Up the Coin Patinating Soluble Compound to the Boiling Point on Gas Stove

Heating Up the Coin Patinating Solution

To put all coins in and out of the boiling compound at once, construct a small coin basket. With wire cutters, I cut a small rectangular section out of a mesh-wire kitchen tray, which is normally used for storing table utensils. And I attached an aluminum wire handle to it (sometimes the dug junk comes in handy). The size of my improvised basket is small enough to fit into the bowl, and large enough to accommodate a dozen of coins.

My Improvised Coin Basket for Submersing Coins into Boiling Solution

Coin Basket for Submercing Coins into Patinating Solution

As soon as the compound starts to boil, immerse the basket with coins into the soluble compound, lower the flames, and boil the coins for 10 minutes to ensure that they all turn dark-blue.

Boiling Copper Coins in Tarnishing Solution

Coins Are Immersed into Boiling Patinating Solution

Rinse the coins with water after you take them out, and dry them with napkins or cloth before doing the next procedure.