Copper is a brightly colored metal often used for decorative purposes, including furniture, artwork and jewelry. Over time, the surface of the copper reacts with oxygen, heat or other aspects of the environment and creates a coating of color, or patina. Although most natural patinas on copper are green in color, it is possible to create a black or dark brown patina. Each treatment produces a slightly different color, so you may want to try several on your copper items to see which result you like best.
Steps
Method 1 of 3: Blacken the Copper with Hard Boiled Eggs
Step 1. Use this method to make small and easy changes
The yolks of hard-boiled eggs can produce sulfur and related chemicals that react with copper to change their color to a darker brown or black. Although this is a more time-consuming method and does not produce such marked results as using the liver of sulfur, you will only need hard-boiled eggs and a closed container.
Step 2. Prepare two or more hard-boiled eggs
Use two or three eggs for copper jewelry, or more if you have several large items or items. Put the eggs in boiling water and leave them for about ten minutes. The smell and the green ring around the yolk are good indicators that the eggs will be able to blacken the copper.
Step 3. Smash the eggs
Use a spoon or other to chop the eggs into pieces. If the container you are using is a bag, it is best to put the eggs in first.
Step 4. Put copper and eggs in a container
Try to keep the eggs from touching the copper if you want to avoid having color spots on the copper. Better to omit the copper objects at one end of the container or on a saucer.
Step 5. Close the container
Close the lid or bag. The container must be tightly closed to ensure that the gases produced by the eggs are concentrated enough to affect the copper.
Step 6. Check regularly
Depending on the freshness and quantity of eggs used, you may start seeing results in twenty minutes or several hours. Check every half hour or an hour, or, if you want the copper to become particularly dark, let it pass overnight
Step 7. If necessary, clean the excess oxide
Use a clean cloth to remove excess color if the copper has become too dark or if you want to create a more distinctive and less uniform effect.
Method 2 of 3: Blacken the Copper with Potassium Sulfide
Step 1. Follow the instructions below to make significant changes
The liver of sulfur, made up of potassium sulfide and related chemicals, reacts with copper to create different colors. While this is a more expensive and potentially more dangerous material than the substances used in the other methods, with this you have a better chance of creating a much darker patina.
Step 2. Clean the copper
Wash the copper in hot, soapy water. Relatively clean copper objects, with no oily sheen or dirt attached, can be cleaned by wiping a cloth or treated with a household cleaner.
Step 3. Buy liver of sulfur in liquid, gel, or dry form
Liver of sulfur can be purchased in different formats. The liquid form is pre-diluted but can only last a few weeks. The gel and dry ones must be mixed with water before being used and if stored properly they can last much longer. Remember that the dry form, sold in pieces or blocks, can release a dust that is dangerous if inhaled.
Step 4. Work in a ventilated area using gloves
Put on latex or rubber gloves before handling sulfur liver as it can irritate the skin. Work outdoors or in a well-ventilated area, especially if you work with dry sulfur liver. The liver of sulfur has a strong and unpleasant odor that you can reduce thanks to adequate ventilation. Wear safety glasses if you have them.
- If the sulfur liver comes into contact with the skin, rinse the affected area under running water for 15 minutes.
- If it comes into contact with the eyes, rinse with running water for 15 minutes and occasionally move the eyelids to expose more of the eye to the water. Seek medical help.
- If you ingest liver of sulfur you must induce vomiting immediately and seek medical help.
Step 5. Dilute the liver with sulfur
The dried sulfur liver must be broken down to a pea-sized piece. The inside will be more effective. Add this piece to a cup (240 mL) of water. In liquid or gel form it must be diluted according to the instructions since the various brands contain different concentrations of liver sulfur or be already pre-diluted correctly.
Cold water and a more diluted solution should work well with the copper treatment also allowing greater control over the color. Hot or boiling water can blacken the copper faster, but never mix the liver of sulfur with hot water because this produces dangerous gases
Step 6. Prepare a baking soda bath in time
The baking soda will neutralize the liver of sulfur thus avoiding to blacken the copper more than it should. Prepare a solution of water and baking soda early so that you can stop the color change whenever you want. In a container other than that of the liver of sulfur, mix one part of bicarbonate with sixteen of water. Use a container large enough to immerse the copper object.
Step 7. Use tongs to dip the copper into the liver sulfur solution
With gloves and tongs, or tweezers for small objects, keep the copper object immersed in the solution of water and liver of sulfur for a short time.
If the object is too large to be immersed, use a brush to apply the solution or pour the solution into a larger container
Step 8. Repeat until you reach the desired color
Remove the copper from the solution and check the changed color being careful not to keep it too close to or over the eyes if they are not protected. Depending on the concentration of the solution and the temperature of the copper you will be able to see every color from pink to black. Dipping it several times in the solution should lead to a darker color ending with a black or gray sheen.
- If the color change is minimal, try heating the copper in a little hot, not boiling water. The higher temperature should cause a more significant change.
- If the color is not dark enough, try mixing 1 teaspoon (5 milliliters) of pure ammonia with the solution. The addition of ammonia should lead to a more red color instead of black.
Step 9. Clean the copper with baking soda to stop the color change
Once you have reached the desired color, immerse the copper object in baking soda for a few minutes. Take it off and wash it in warm soapy water.
- If the color change was excessive or if you want to create a less uniform and older effect, lightly scratch the patina with steel wool or a paste made with baking soda and a few drops of water.
- Once the baking soda is finished, the liver of sulfur can also be added. This will neutralize it and allow you to throw it away in the sink.
Step 10. Treat the copper with wax or lacquer to preserve its color
Any metal wax or lacquer can be applied to the new patina according to the instructions. This will prevent or slow down any further color changes as long as the wax or lacquer is kept clean and is not scratched off.
Method 3 of 3: Color the Copper Green or Brown by Making Your Own Solutions
Step 1. Create your own solutions to obtain particular colors
the natural green patina can be imitated with an ammonia solution, while the dark color of the 1 cent coins can be created with bicarbonate and water. Since the application of the two solutions is similar, they are both described in this section.
Step 2. Clean the copper
Wipe the object with a clean cloth. Dirty copper objects should instead be washed in hot soapy water, then dried thoroughly.
Step 3. Follow safety procedures if you use ammonia
If you are trying to create a green patina you will have to use ammonia. Work outdoors or in a well-ventilated area or with a fan. Ammonia vapors can be toxic, which is why ammonia should not be handled in closed spaces. The use of protective gloves and goggles is recommended.
If you want to create a brown patina with water and baking soda, there is no need to take any precautions
Step 4. Use ammonia to make a green patina
Take 2 cups (or 500 ml) of white vinegar, half a cup (or 125 ml) of non-iodized salt, and one and a half cups (or 375 ml) of pure ammonia. Ammonia can be found in various stores, just be careful not to take the less powerful detergent.
The more salt you add, the greener the patina will be
Step 5. Prepare a solution to have a brown sheen
This solution will give the copper a dark brown color, typical of one cent coins. Simply stir some baking soda in a hot water bottle, one tablespoon at a time, until it has dissolved.
Step 6. Spray the solution onto the copper
Use a spray bottle to apply the patina to the copper surface. Spray harder for an even result instead of stripes or patterns.
Step 7. Keep it in a humid place for one to eight hours
It will take some time for the patina to form, keeping the object in a damp place will speed up the process. If you keep copper in a dry place, use a plastic bag or sheet to cover it without touching the surface. This will help maintain humidity.
Step 8. Reapply the solution if the patina wears off
Depending on the environment in which the copper is kept and how often it is handled, the patina can wear or fade before setting permanently. If this happens, reapply the solution as before, on the entire surface or only where the patina has come off
Green patina tends to be dusty and easier to peel off than brown patina
Advice
- If you use the solution for the green patina, reduce the salt to decrease the intensity of the green.
- Long-term exposure in a humid environment will cause slow oxidation of the copper which will create a green patina. Consider leaving the copper object outside to speed up this process.
- Copper will not react to magnets. If a magnet sticks to your object then it is copper plated or made of another material that may not react to the treatments described.
- Liver of sulfur should be stored in an airtight container placed in a dark and dry place.
- If you have access to a chemistry laboratory, consider trying these formulas to obtain patinas of various colors. Remember these are obtained from various sources without rigorous testing and should be applied on hidden corners first.
Warnings
- Wear safety equipment such as work gloves, goggles and masks, minimize skin exposure and avoid the harmful effects that these products can cause.
- Solutions for blackening metals can be dangerous for the eyes, skin, respiratory system. Have a first aid kit on hand.
- The solutions for blackening metals, waste and rags used for cleaning are hazardous waste and must be disposed of in accordance with current regulations.
- Blocked sulfur liver is flammable and dangerous if inhaled.
