Why Copper turns Black or Green? / Copper Tarnishing

Copper turns black or green

Copper is one of the good metal. It also acts as a mineral in the environment. But at some point, Copper is a reactive metal. Copper being an inevitable metal will turn into a black or green color. What could be the reason behind the change in color?

The reason behind the change in copper bottle/vessel color is due to “oxidization”. In the process of oxidation, copper reacts slowly in the presence of oxygen, resulting in copper oxide. It’s a chemical reaction that is completely natural. Thus, making your copper vessel/bottle layer oxide.

This process takes place when a copper bottle is left exposed to air and water. It leads to the formation of a thin, green layer on the surface of the metal. Acts as copper’s protective layer.  

This thin green substance is named copper carbonate or “green patina”. It does not affect the quality of metal. The oxidation process takes a gradual time to convert copper into a green patina. And before turning green, copper may turn into a black or brown color substance. 

Patina’s Symbolic

The patina is symbolic of a sign of age, which is highly prized as it raises copper metal value. Furthermore, protecting copper from other elements. The best example is of Statue of Liberty, which is of green coloration. But, from the actual fact, Lady Liberty is made of copper. It has formed a Patina formation with time. Exposure to air and water for a far longer time.

Due to this, many artists even treat copper surfaces/items with acetic acid to form copper acetate, also known as Verdigris. It is soluble and it only gives copper a green color coating. This is not as durable as a natural patina. Food items comprising the acetic compound are likely to induce instant corrosion when in contact with copper cookware. Food includes items like milk, wine, or vinegar, etc. The corrosion is Verdigris.

To a concern, this issue is more than just aesthetics. Where Copper tarnishing is just inevitable. Oxidation of copper will limit its heat conductivity. The copper vessel gets an effect. So, take proper care of your vessel. Or else clean it very well.

How to get rid of the Patina or Green layer?

The green patina so formed can be prevented by keeping your copper vessel/bottle/utensils into direct sunlight. Because of Oxygen, the formation of green patina takes place. Thus, preventing oxygen to come in contact with the copper metal will help you to stop the patina formation.

Another great way to get rid of patina is to clean your copper bottle with a solution of salt and vinegar, once a week. Be gentle, while washing the solution onto the vessel. Avoid harsh scrubbing. The patina on the surface of the item should be wiped off to avoid watermarks.

Circumstances Affecting Copper: How & Why?

  1. Oxygen – One of the most inevitable and natural types of tarnish happens in the presence of oxygen. Copper oxide formation takes place when copper and oxygen ions react. The process is very slow when comes to contact with dry air.
  2. Human Touch – The quickest way in which copper can tarnish is the human touch. The oil present in our skin is responsible for it. As copper is inevitable, there is a need for proper and regular cleaning of copper vessels and utensils.
  3. Moisture – Moisture catalysis the oxidation process. It enhances the reactivity of copper which leads to corrosion and patina formation. After that, wipe off all the water from the washed copper utensil or vessel. Instead of letting them dry on their own.
  4. Dust – Dust particle has the formation of dead skin cells and debris from both humans and pets. Tarnish happens more quickly as the debris contains a chemical that reacts with copper metal.

Some more circumstances include –

  1. Acidic Substances – The surface of copper easily reacts with acidic substances. This type of corrosion is highly soluble, which leads to the formation of toxic copper salt in the food. Subsequently, it is said not to use the copper vessels for acidic substances like milk, vinegar, or wine, etc.
  2. Heat and Chemical – Tarnishing of copper can happen with certain cleaning products and heat. Heat makes copper more reactive, while some products contain substances that react with copper. It is not recommended to place copper utensils in the dishwasher. However, to avoid such damages, clean them in more copper-friendly ways.


Since the discovery of copper, drinking water out of copper vessels is been practiced. If you properly follow the precautions then drinking water stored in a copper vessel can be a safe and healthy practice and you can prevent your copper from turning black or green. Though it will be based on the assumption that you are using quality copper vessels. In addition, it is also important to ensure that you do not store acidic substances in copper vessels.  

Copper tarnish is inevitable, but there are many easy ways you can clean it and prevent it. Make sure to clean your copper bottle regularly with proper care to enjoy the many health benefits of copper-infused water to the fullest potential. 

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