Why Do Bronze And Copper Castings Sometimes Turn Green?

The beauty of a hand casting, particularly one made out of bronze or copper, is that it is a permanent reminder of an often fleeting moment.

The first few moments of a baby’s life are beautiful, and having a memento from when your child was so small and tender can immortalise such a meaningful part of your life with materials that last for a very long time.

However, some materials, such as bronze and copper, will change over time, both of which often transform from a glimmering orange-brown to a dull but extraordinarily vibrant blue-green colour.

This is a natural process known as patination, which, whilst it can often be used to describe any type of aesthetic ageing or distressing, specifically describes how bronze sculptures develop a blue or green surface layer as the result of oxidation.

This is most commonly seen on statues left outside, with the Statue of Liberty in New York possibly the most famous example in the world, and so associated with this particular patina that many people do not realise it was not originally that shade of blue.

As with rust development, water reacts with carbon dioxide and copper, which creates a blue copper carbonate that lies on top of the bronze. It can be cleaned off, but many people like the look so much that they not only leave it on but will sometimes deliberately apply it.

Part of this is related to the Japanese concept of wabi-sabi, or an appreciation of impermanence and transition. The word “sabi” translates from Japanese into patina, which is a more direct connection to patinated bronze.

This concept is often why people want casts in the first place; they want a memento of a transient element, and to truly appreciate every moment with a child, as the palms captured by the cast will continue to grow until adulthood, and they will never be as small and as young again.