Patina on Concrete

I wrote about casting small parts of camera lenses back on June 21, 2009. Now I'm experimenting with applying a chemical patina to some new castings in that series.

 

Concrete Pins: concrete, copper leaf, patina, 2010

The effect is just what I wanted: to make the camera parts look almost as if they had been buried and dug up. After the castings were cured (about two weeks), I applied copper leaf to the smooth lens areas, and left them so that the gold size was completely dry. Then  I painted on a thin wash of copper nitrate solution, exactly what I use for patination of copper and brass jewellery. To "set" the patina, I heated it very gently with a small propane/oxygen flame. Some of the patina is a very pale greenish blue, some is a light brown.  The black colour is an earlier application of dyed cement that was rubbed in, rubbed off and allowed to cure.

There is the potential when doing this for water trapped in the concrete to turn to steam and either crack the concrete or cause a mini-explosion, so I always were face protection, and never heat the concrete beyond what I would call a skin-burning temperature. And always heat the pieces slowly and evenly. When the colour is right, don't quench them in water, but let them air cool, or they might crack. I finished the pins with a flat acrylic sealer to make the patina waterproof.