Art Articles & Reviews

} Copper sulfate for etching both zinc and aluminium Printmaking Series - Part 3 of 21 By Nik Semenoff Nitric acid is a dangerous chemical, but has been the main mordant used by etchers for centuries. There are many mordants with acids being the main ingredient. Recently, ferric chloride has become more common for copper as this chemical is used in making electronic circuit board. Using it to etch zinc is not a good idea but printmakers try as they look for safer methods. Aluminium is generally not used much for intaglio as artists consider it incapable of giving fine detail or large editions. Because of the cost of zinc plates, one of my students felt she could not finish her assignments and wonder if a cheaper metal could be used. Since I required only six for an edition, aluminium would be good enough, but we were using nitric acid as mordant for zinc or copper. We chose not to use ferric chloride and stannous chloride proved to be too expensive. Falling back on my experience, but somewhat limited knowledge of chemistry, I looked at copper sulfate as a mordant. Within a short time I found the problems of using aluminium and the best additives for the copper sulfate solution, so that by the time I was to teach a summer session class, I had a working process. It was eventually published in an international referred journal and has become the basis for of other printers' work with copper sulfate. Copper sulfate is one of the heavy metals and restricted in some jurisdictions, especially where grapes are grown; used with lime (Bordeaux mix), it has contaminated ground water. When used as a mordant and recycled a number of time, it can eventually be disposed of as a solid in regular waste. Check with local restrictions. Common salt is added to increase the activity of the mordant for both zinc and aluminium. When etching only aluminium, a small amount of sodium bisulfate is added to prevent aluminium hydroxide gel forming - this can be obtained from Sani Flush at the grocery store. Yoko Imabayashi Most resists will work, so all common etching technique can be employed. The action on aluminium in an open bite produces a rough surface so an aquatinting tone can be achieved without rosin. During etching, there is a very small amount of hydrogen produced that constantly pushes out the fine copper particles created from the electro-chemical reaction. So that unlike ferric chloride, the plate does not have to be etched upside down. As the copper is removed from the bath, it will lose its' blue color, indicating how strong it still is. By adding more copper sulfate, the bath can be extended. An remarkable thing happens when the bath sits for a while. The sulfate radicals in the solution attack the fine particles of copper and returns the bath back into a stronger mordant as it recycles itself. Yoko Imabayashi It works very well on zinc and the best replacement for ferric chloride when etching this metal. Some are concerned with the black surface left where the etching takes place. The mordant works just as fast as any other and can be mixed so strong that the reaction can cause the solution to boil. ________________________________________________ Copyright © 2004 Nik Semenoff Nik Semenoff Artist-in-residence University of Saskatchewan Visit Nik Semenoff's website at duke.usask.ca/~semenoff/ for more information.