Corrosion art |

Activity – using electrochemistry and corrosion for art and design

Architects, jewellers and artists often oxidise copper to make beautiful blue/green ‘patinas’ on the surface of metal surfaces, such as the Mermaid fountain (Birmingham, UK) and the Statue of Liberty (New York, USA). This is the same chemical process that causes corrosion. When the copper oxidises to form copper ions, these form complexes in solution that can vary in colour, depending upon what molecules (ligands) bind to them, i.e. [Cu(H₂O)₆]²⁺ is blue, [CuCl₄]^2- is green, [Cu(NH₃)₄(H₂O)₂] is a dark blue.

AIM

To make your own patina on a copper surface

YOU WILL NEED

Copper metal (sheet metal or a piece of pipe)
fine sand paper
plastic box with lid (large enough to fit your copper in)
paper towel
10% ammonia solution (i.e. for cleaning)
garden wire
table salt
mustard (optional)
spray bottle
spray laquer (i.e. clear laquer /top coat spray, suitable for metals)

PROCEDURE

In order to oxidise the copper in a short space of time, we can use ammonia:

Take the plastic container and put some paper towel in the bottom. The copper will need to be suspended in the container so drill or poke holes in the sides of the container large enough to slide a bit of wire through (any type of wire will do). Depending on what you wish to patina, you will have to adapt this hanging system, two wires will hand a sheet evenly. Take the plastic container outside (or in a fume hood) and carefully pour in some ammonia solution into the bottom, to moisten the paper towel, and put the lid onto the container.

In order to prepare the copper, it needs to be free of oil/dirt/oxides. Wash the copper with washing up liquid and dry, and then rub it with very fine sand paper. Once this is done, handle the copper on the edges, to avoid getting oil from your hands on the surface.

Carefully place the copper into the container, so that it hangs (using the wire) over the ammonia -soaked paper towel. Dissolve a few teaspoons of salt in a cup of water, and using a spray bottle, spray the upper surface (this is where you are developing your patina) with the salty water. If you wish to mask parts of your copper, you can use a paintbrush and mustard to coat the copper where you do not want the oxidation to occur.

Leave the copper to oxidise for several hours in the chamber, with the lid on. Once you are happy with it, remove the copper and leave to dry. (If you have used mustard, this will turn black and crusty, and will need to be gently removed under running water). To preserve the patina, spray the finished piece with clear lacquer – do this outside, or in a well-ventilated space.