First steps in making pigments on galvanised iron strips for a Wave using copper and lead salts.
Making a painting
The photo on the right shows the early stages of making an image based on the Whirlpool Nebula.
The black pigment was made first by releasing copper sulphate onto the surface from a plastic teat pippette. The grey areas were made using lead nitrate.
The lead deposited oxidizes, making white lead hydroxide and (eventually) white lead carbonate, (the painter's lead white). Never lick one of my pieces!
The lead and copper bind chemically to the metal beneath, making a foundation for other pigments.
More solutions can then be added to this, to make (say) copper carbonate (malachite green) or lead chromate (chrome yellow).
Patinage is the word I use for making pigments on galvanised iron sheet. It is actually the French word for ice-skating, so if you can think of a better word, do let me know.
I invented this technique on my City College course. We were expected to be original, to make use of our experience, and to explore the ‘making of marks’. As a chemist I knew a fair bit about making pigments and paint. Some of my students had made and investigated their own, and even painted with them. I realised I could make pigments using chemical reactions with galvanised iron. This would be new.
Galvanised iron is iron coated with zinc. It covers the iron and stops it from rusting, (Fig 1 below). It does this because it is more reactive than iron, mopping up water and oxygen that would otherwise rust the iron underneath.
However, because zinc is so reactive, it lays itself open to attack. To make a mark I treat the zinc with a solution of a heavy metal like copper sulphate, (Fig 2). The zinc goes into action, dissolves, and replaces the copper in copper sulphate. The copper itself is deposited on the metal, a black layer of tiny copper crystals, (Fig 3).
zinc metal + copper sulphate copper metal + zinc sulphate
I have made many colours, testing them and keeping notes on colours and changes. Back in the lab again!
As the pigments dried, other salts in the sludge crystallized, often as a white powder. I had to wash them away to get the colour I wanted.
When dry, the surface is powdery, so I fix the pigments in place. I have used artists spray-on fixative, but I now use a polymer dissolved in acetone that penetrates all the pigments really well and binds everything in place.
Corrosion pigments on an iron pier at Gt. Yarmouth