How to Apply Patina for Copper Coins

Knowing how to apply patina to a copper coin can make the difference between a rustic-looking, collectible coin and a coin that will barely pass for acceptable currency. According to the Cartage website, a website that specializes in precious metals, patina is a form of oxidizing or tarnishing that forms on the surface of most metals, such as copper, bronze and silver. The coating of patina does not increase the coin's value; it's simply for aesthetic reasons.

Things You'll Need

• 250 g copper nitrate
• 8 g silver nitrate
• 6.5 ml citric acid
• 5 large bowls
• 3 liters room temperature water
• 3 paintbrushes
• 20 g copper sulphate
• 5 g potassium permanganate
• 70 g potassium chlorate
• 100 g ammonium chloride
• Acetone
• Soft sponge
• Degreasing soap
• Hot water
• Oven
• Oven safe bowl
• Tongs
• Washcloth
• Polishing cloth

Instructions

Making the Patina

1. Add 200 g of copper nitrate, 8 g of silver nitrate, 6.5 ml of citric acid and 1 liter of water to a large bowl. Mix the solution with a paintbrush to make an old bronze patina mixture.

2. Add 20 g of copper sulphate, 5 g of potassium permanganate and 1 liter of room temperature water to a large bowl. Mix the solution with a paintbrush to make a gold-brown patina mixture.

3. Add 70 g of potassium chlorate, 50 g of copper nitrate, 100 g of ammonium chloride and 1 liter of water to a large bowl. Mix the solution with a paintbrush to create an olive patina mixture.

Applying the Patina

1. Pour acetone into a large bowl and place the copper coins into the bowl. Scrub the coins in a circular motion with a soft sponge to help degrease the copper coins.

2. Remove the coins from the acetone solution and wash them in a large bowl with a degreasing soap and warm water solution. With the same sponge, scrub the coin's surface and crevices in a circular motion. After washing the copper coins thoroughly, leave the coins out in the sun to dry.

3. With the olive mixture, cook the solution before using it. Preheat your oven to 150 degrees and add the olive mixture to an oven safe bowl. Drop the coins into the olive mixture, put the mixture into the oven for 15 minutes and take the coins out of the mixture and let them dry. With the olive patina, clean the salt that will form on the coin with a washcloth and wait 12 days for the patina to appear.

4. Paint the old bronze mixture on the copper coins. Dry the coins, repeat the old bronze treatment 3 to 4 times, and then use a polishing cloth.

5. Paint the gold-brown patina on the coins. Let the solution dry for 24 hours and then rinse the coins in hot water.

References

• Cartage: What is Patina?
• Metal Detecting World: Artificial Patination of Copper, Zinc and Iron