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Verdigris: Understanding the Green Goo

Verdigris: Understanding the Green Patina (or Green Goo) on Electrical Cables and Light Sockets

If you’ve ever seen a green discolouration on the surface of electrical outlets, you may have wondered what it is and whether it’s something to be concerned about. The discolouration is commonly referred to as “verdigris,” a term from the Old French word for “green growth.” In this article, we’ll take a closer look at what verdigris is, how it forms, and what impact it can have on electrical cables and property.

What is Verdigris?

Verdigris is a green patina that forms on copper and copper-alloy surfaces due to the action of weathering and corrosion. The patina is made up of copper carbonate, copper chloride, and copper hydroxide. These compounds form as a result of a chemical reaction between the copper and the elements, such as oxygen, carbon dioxide, and sulphur compounds. The exact composition of the patina will depend on the specific conditions of the environment in which the copper is exposed.

Verdigris - green goo

How Does Verdigris Form on Electrical Cables?

Electrical cables are often made of copper; when exposed to the elements, the copper conductors can develop a green patina over time. The patina forms as a result of the same chemical reactions that occur on other copper surfaces. The process can be accelerated by exposure to high humidity, salt spray, and other harsh conditions.

What Impact Does Verdigris Have on Electrical Cables?

The discolouration of the verdigris is generally considered cosmetic and does not affect the performance or safety of the cable. However, if the verdigris is severe or the cable is damaged, it may be necessary to replace the cable to ensure proper electrical function. In addition, verdigris can increase the resistance of the copper conductor, which can lead to an increase in the temperature of the cable. This can be a fire hazard if the verdigris is severe and the cable is damaged.



Verdigris is common on older copper electrical cables and looks unsightly; however, if the patina is severe or the cable is damaged, it may be necessary to replace the cable and socket to ensure proper electrical function and safety. The ongoing issue with Verdigris is that it can stain the wall, as highlighted in the photo above.

If you do have Verdigris about your home or office, it is important to keep it away from your eyes and mouth (not that you should be licking any sort of electrical point); more importantly, minimise and keep the little humans in your home away from any form of Verdigris.  Verdigris can cause burning on the more sensitive parts of the body, such as the eyes.

If you have concerns about your property, then a simple insulation resistance test can be carried out by Napier Electric Company. Let us know how we can help. 

Note: Verdigris occurs in older wiring; today’s standards have an antioxidant to minimise degradation.


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