Experimenting with etching aluminium

Normally etched zinc or copper plates are used in the printing process. A copper plate, with a fine layer of aquatint allows you to achieve subtle ranges of tone. This is the process that I have been developing over the last year. When I had my exhibition over the summer, I displayed one of the copper plates and many visitors were interested in the technical aspects of producing the prints. Although the plate is a means to an end, it is in itself a lovely object.

I wanted to experiment with etching aluminium, as this was the metal that was predominantly used to fabricate the outer skin of the wings and fuselage of the Spitfire and Hurricane. Where as nitric acid is used to etch zinc and ferric is used to etch copper, I would have to mix a solution of copper sulphate and sodium chloride (cooking salt) to act as a mordant on the aluminium. On researching this process, I found it was often referred to as 'non-toxic', however all the usual precautions will need to be taken - gloves, mask, goggles, apron etc.

I started by treating the surface of the metal with wire wool to create a 'tooth' which should help the etching process - leaving a untreated strip as a 'control'. I then marked off thin strips on two of the plates so that I could gauge a succession of different timed etches.

On a third plate, I drew out a section of a quote from one of the Castle Bromwich workers - reversed, and then painted the letters with a resist . This should ensure the plate only etches the untreated areas and will leave the lettering untouched.

I mixed up the copper sulphate saline solution in a well ventilated area, in a tub that would be big enough for the plate to be completely submerged. I had a large tub of water next to this to wash off the solution.

I started by dipping one of the marked off plates for 2 minutes. There was a strong chemical reaction - rapid bubbling and a large build up of a rust coloured crust.

This had to be washed off the plate, which was then dried before a strip was stopped out with resist. The plate was then etched for a further 2 minutes and the process repeated until the last strip was left exposed having been etched for a total of 10 minutes.

I then etched the plate with the quote for 4 minutes. you can see on the image below the resist has done its job.

I then tried applying the copper sulphate saline solution directly to the plate with a brush. I applied strips of the solution at one minute intervals for a total of 10 minutes.