ARTICLE PUBLISHED IN
Issn 0960 9253
Etching: Friedhard Kiekeben gets to grips with the science of non-toxic intaglio printmaking and explains his own pioneering discoveries
Nowadays, it seems, we are reassured by the ‘science bit’ in marketing. Any product is expected to have the seal of approval from a man in a white lab coat; from shampoo to yogurt drink. Generally the item in question is not going to do us any harm, but the science is reassuring. It is ironic that we seem less stringent about genuinely harmful materials because we’ve been using them for years ‘without any ill effects’.
In all likelihood I would have used bucketfuls of nitric and solvents over the last 11 years, in my practice as an artist, if I hadn’t thought more about the science bit. I suppose I must have absorbed my dad’s interest in chemistry (he was a science teacher in Frankfurt) and this combined with a natural curiosity about the stuff of printmaking:
Was there an alternative to acids? What do you get when you cross a lemon and iron chloride? Can you etch with salt?
It wasn’t so much that I wanted to meddle with the history of printmaking, just some of the ingredients. We are preoccupied by healthy living and I wanted to apply similar principles to healthy working. Meeting printmakers like Keith Howard and Robert Adam who were already developing ideas and practice in line with safer printmaking, galvanized my own experiments.
A lot of my methods are well documented and widely used. However, as with all processes they are – quite rightly - open to questioning. As my complete system of Metal Salt Etching would feature in Keith Howard’s The Contemporary Printmaker (2003) I wanted it to be tested by two leading experts in environmental chemistry. I have always taken advice from scientists, but here was an opportunity to confirm the many benefits offered by this new approach to etching: And here comes the Science bit…
Metal salt etching comprises two kinds of process for the entire spectrum of metals suitable for intaglio printmaking and etched sculpture. The Edinburgh Etch contains the reddish ferric chloride and it etches the warm colored metals; copper and brass. The Saline Sulphate Etch, based on copper sulphate, etches the silvery metals; zinc, mild steel, and aluminum. Both these salts have been used for centuries but what had been overlooked is that their potential for etching is not fully harnessed when used without a catalyst. In fact, I would argue that this knowledge remained unexplored because metal salts were judged as if they were acids. But metal salts do not corrode metal through the destructive and harmful processes that typify acid etching: by contrast they owe their etching properties to electrical attraction in which atoms of the metal plate are elegantly removed by the metal compounds that are dissolved in a salt solution.
Today we know that this is an electrical kind of chemistry which is more akin to the workings of a battery than to the corrosive action of strong acids. Think of the rabbit in the Duracell ad: a battery on a full charge will give plenty of electrical energy while a weak or depleted one will soon stop moving an electric toy rabbit. The difference lies in the strength of the electrical charge: the rabbit with the biggest charge wins.
In 1997 I invented the ‘catalyzed’ version of ferric chloride, The Edinburgh Etch, in which a small addition of citric acid literally dissolves the sedimentation of the iron salt; thus creating a much more potent, yet safe, mordant. This process has since been adopted throughout the printmaking world and etchers have likened its crisp biting characteristics on copper to Rembrandt’s (toxic) Dutch Mordant.
Now many printmakers know what lemons and iron chloride can do together.
Soon after I published this research in Printmaking Today the electro etching expert, Cedric Green, noted that The Edinburgh Etch is ideal for etching copper but that a solution based on copper sulphate, The Bordaux Etch, should be used for a safe zinc etch. Intrigued by Cedric’s ideas I introduced copper sulphate into my own research program. Trials showed that a straight copper sulphate solution makes a good mordant for zinc (but not for aluminum) but consumes a large amount of copper sulphate crystals.
I realized that once again the right catalyst would accelerate and improve the efficiency of the etching process. As before I systematically introduced different ingredients to the process and monitored their effects, quantities and by-products. I had a pretty good idea that due to its conductive effect in water, simple cooking salt (sodium chloride) might be the key ingredient. Most of my time was spent researching the perfect ratio of salt to sulphate. The addition of an exactly equal quantity of salt to copper sulphate dramatically increases the speed, quality and longevity of this new etching solution: The Saline Sulphate Etch.
This solution now provides a universal etching bath for all three silvery metals: Zinc, Aluminum and Mild Steel, and will no doubt become an extremely useful method in the repertoire of printmaking. The Innovative Printmaking students at UCC Chester can’t get enough of The Saline Sulphate Etch and use it on a daily basis, and in my own work it enabled me to etch the large scale aluminum sculpture ‘Shatter-Ice’ shown here. For anyone who loves the physicality of etching it is such an exciting and satisfying process to use.
A recent conference on non-toxic printmaking in Barcelona brought an opportunity to meet Cedric Green, father of The Bordeaux Etch, who wholeheartedly approves of the latest addition to the metal salt method. During the same event Eva Figueras presented evidence that Goya already etched zinc in copper sulphate. Unfortunately for printmaking, metal salt etching, for a number of historical and technical reasons, did not become mainstream practice until today.
In 2003 I presented my complete research on the Metal Salt Etching system to the chemistry professors Dr Paul Craig and and Dr Paul Rosenberg at the Rochester Institute of Technology, New York, for final testing and assessment. Dr Craig took an empirical approach and together we etched plates under laboratory conditions, making sure all relevant data such as plate size, etching times, mordant strength etc were faithfully recorded. Dr Rosenberg never needed to visit the print studio. He took an analytical approach in which all variables and by-products of the chemical reactions were determined through chemical formula and calculations. The results of both strands of investigation were then formulated into a safety assessment for Metal Salt Etching which is published in The Contemporary Printmaker but can also be found on my research web site: >www.chester.ac.uk/art/kiekeben<
The assessment states that: ‘In the past metal etching for the purpose of printing or art was typically done with nitric acid, which has harmful vapors and is extremely caustic...The Edinburgh Etch adds one new ingredient to the etching bath: citric acid. Etching...is much more rapid and reproducible than the original ferric chloride etch...The Cu2 will have a tendency to form a complex with citric acid…increasing its solubility. The hazards associated with the Edinburgh Etch are dramatically less than those associated with nitric acid. In fact it could be safely used in an open studio or laboratory.
The Saline Sulphate Etch is recommended for etching aluminum or zinc (or mild steel). In the absence of sodium chloride, a copper etch of zinc is characterised by high levels of insoluble hydroxides...which may clog the etching process, for reasons like those proposed previously for the Edinburgh Etch.
For the printer or artist both these systems are mild and much safer than the traditional nitric acid bath for etching of metals, especially if proper precautions are taken (i.e. no etching of aluminum with ferric chloride) and when exhausted materials are disposed of properly. To the chemist, these are very nice systems, which are highly complex...There is not much published information on these systems…All would bear some study from the chemical perspective…There does not appear to be any significant or major chemical hazards associated with the chemical processes employed here, although a reaction between aluminum and iron (chloride) could lead to explosive results.’
The reaction diagrams provided by Dr Craig and Dr Rosenberg clearly show how the new metal salt solutions increase the electrical voltage that is present in a pure ferric chloride or copper sulphate bath. The simple addition of measured quantities of crystalline lemon juice (citric acid) and cooking salt (sodium chloride) respectively, produces an etching environment safer and more effective than the traditional nitric bath – ‘and that’s the science’.
Metal Salt Etching: Basic Recipes
Saline Sulphate Etch
To etch zinc, aluminum, mild steel
Mix 100g copper sulphate crystals
with 100g cooking salt
dissolve in 1 litre of warm water
To etch copper or brass
Dissolve 250ml of citric acid crystals
In 1litre of warm water
4 litres of saturated ferric chloride solution
(strength about 40%, or 42-48 BE)
(multiply or reduce amounts while retaining correct ratios)