Copper has been in use for a very long time. The earliest archaeological pieces of evidence can be traced back to 10,000 years that indicate, it was a common metal known to most of the early civilizations. Historically, copper has been used for various purposes- as utensils, tools, ornaments, weapons, and sculptures.
Even though the use of copper has declined over the years, given its bright red-orange lustre and cool aesthetic properties, it still remains one of the most preferred metals for the use of cookware, jewelry, and decorative purposes.
Like most metals, copper also undergoes oxidation in air. It turns black due to the formation of copper oxide. To retain the natural shine of copper items, you need a mild acid that will cancel the basic copper tarnish, without destroying the metal. This can be done by a variety of methods, but before jumping into that, let’s know why and how copper tarnishing takes place.
copper vs citric acid
Why does copper tarnish?
Pure metals react with air, water, and chemicals to slowly degrade and corrode over time. Similarly, copper also reacts with the surrounding environment to tarnish in a multi-step process where it first becomes a deep red color, then a black film, and finally turns into a bluish-green patina.
When copper metal is exposed to oxygen in the environment, copper (I) oxide forms, which is red in color.
2Cu + ½ O2 → Cu2O
Cu2O is again oxidized to form black-colored CuO.
Cu2O + ½ O2 → 2CuO
This CuO reacts with water, sulphur, and carbon dioxide to form a greenish-blue covering referred to as patina.
You can do an experiment to observe the successive oxidation stages of copper by placing a sheet of copper on a burner. Observe the copper turning red, then black.
The final stage of patination, i.e formation of a blue-green layer on copperware, takes several years.
This darkening and change of color can be both undesirable and harmful. That’s why it becomes important to clean the copper items every once in a while.
Different ways to clean copper vessels:
1. Lemon and Salt to Clean Copper Homeware
Lemon is a common homemade ingredient used for combating copper tarnish.
Copper oxide dissolves in citric acid that is abundant in lemons. Salt added to the lemon, makes it easy for scrubbing off the tarnish.
The citric acid present in the lemon is used to neutralize the basic copper carbonate which forms black copper oxide. That is why the tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic luster.
Simply, apply some salt on the cut side of the lemon, and rub it gently on the copper vessel.
You can also leave the paste on the stained parts for some time. This helps to regain the characteristic shine of copper.
2. Baking Soda and Lemon
Baking soda should be used with vinegar or lemon juice, to clean the copper surfaces.
The natural abrasive property of baking soda makes it a good cleaning agent for tarnished copper. The acid present in vinegar or lemon juice, paired with the gritty texture of baking soda will work wonders for your tarnished copper vessel. This method is harmless, food-safe, free of harsh chemicals, and also inexpensive.
3. Using Vinegar or Acetic Acid
One of the most commonly used ingredients in the kitchen, vinegar acts as a fantastic cleaning agent for copper. Vinegar contains 5- 8 percent acetic acid, which dissolves the unwanted copper compounds, giving it a shiny finish. You can also mix it with salt, baking soda, and flour to make a paste.
4. Acetone
A common chemistry lab ingredient, you must be familiar with acetone which commonly serves as a solvent. Dip the copper utensils entirely into the acetone solution to clean it. You can also use it in the same way as you use a nail polish remover, which is also primarily made of acetone.
5. Tartaric Acid
It is generally used in combination with acetic acid, to serve as a potent cleaning agent for copper surfaces. It is used for cleaning tough and stubborn copper stains.
How to Prevent Copper Utensils From Tarnishing?
Prevention is always better than cure. Yes, the age-old proverb stands true in this case too.
To prevent tarnish:-
Coat the copper with a protective film of lacquer or copper polish to prevent its exposure to the atmosphere. Be careful though, it is only advisable to use a copper polish, wax, or lacquer covering for decorative items. None of these layers are suitable for cookware.
Dry the copper vessels as soon as you wash them. Use a cloth or dryer. Don’t allow it to air dry
Frequently dust and wash the surface of copper utensils with warm soap water. After washing dry it immediately.
You can clean the outside of copper utensils with lemon or vinegar, and then wash it off and dry.
To clean inside, boil one tbsp of salt and one cup vinegar. Let it remain inside for a few minutes, then scrub and rinse.
Precautions to Take While Dealing with Copper Vessels
Do not use harsh chemicals or very strong acids to clean copper.
Wear gloves when you are cleaning tarnished copper pieces, as the oils from your hands will tarnish the freshly cleaned, exposed copper surface
Don’t heat food in an uncoated copper vessel. Do not store any sour substance in them
The artificial cleaning agents should not be used to clean copper cookware or drinking vessels as they are harmful to the digestive system when ingested along with food or water.
Conclusion
By the end of your reading, you can successfully demonstrate an experiment for cleaning a tarnished copper vessel. You can also show the chemical reaction that takes place while copper tarnishes. Thus, you learned about an important property of one of the most widely used metals in our day-to-day life.