My most recent work is influenced by my research into the use of electrolysis as a safer alternative to traditional acid etching.Through the research I found two further electrolytic processes that had been used extensively by artists in the nineteenth century in both printmaking and sculpture. These were stereotyping and electro- forming. I now use both of these processes in my practice.
As I am often asked ‘how did you do that? about my work I thought it would be useful to offer a brief description of each of the processes here. It is quite difficult in the middle of an informal gallery or studio conversation to offer an off the cuff brief description of these processes. The Processes are:
- Saline Sulphate Etching
Saline Sulphate Etching.
Copper sulphate was one of the first mordants used to etch metals. Abraham Bosse who published the first manual on intaglio etching in 1645 gives a recipe in it that is similar to saline sulphate recipe promoted as a ‘safe etch’ today. It is also thought to be the etchant in use in Goya’s and his contemporaries studios.
The Technical Bit
Saline sulphate etching is a galvanic process.
The above ingredients produce a galvanic cell.
The electrodes consist of the two metals. The cathode is the copper sulphate, the anode is the aluminium plate and the electrolyte is the sodium chloride in solution.
The electrodes consist of the two metals. The cathode is the copper sulphate, the anode is the aluminium plate and the electrolyte is the sodium chloride in solution. The copper ions from the copper sulphate create a powerful electrical potential that attracts atoms away from any exposed areas of the aluminium cathode. The etching potential is dependent on the level of copper ions in the solution; the more there are, the higher the potential. The process that produces and transmits the electric charge that facilitates the migration of the metal ions is contained within the solution of the galvanic battery or passive etching cell. The larger the bath is relative to the size of the plates the higher the electrical charge will be, enabling more etching to take place over a longer period.
Saline Sulphate Etchant
Copper sulphate also known as blue stone, or cupric sulphate, is a blue, odourless crystalline solid that dissolves in water. It can be purchased from agriculture suppliers and garden centres but it is best sourced as copper sulphate anhydrous from chemical suppliers as the agricultural version may contain other ingredients.
The major advantages of saline sulphate over the traditional acid etching are:
· Saline sulphate etching is an electro chemical process rather than a traditional hazardous acid reaction
· No noxious gasses are produced
· In normal use volatile reactions are unlikely
· The metal oxides and hydroxides are released and float to the surface of the mordant and do not clog the bitten line.
Saline Sulphate Etchant
The etchant can be used safely in an open studio, class room or domestic workshop. It can be used to etch Aluminium, mild steel and zinc.
The recipe for saline sulphate used on this course is:
10 litres of tap water
1k copper sulphate
1k sodium chloride (table salt)
500g sodium gluconate (this is not an essential ingredient).
Sodium gluconate is a chelating agent and as such stops the development of aluminium hydroxide that slows down and eventually stops the etching process
Electro-Etching or galvanic etching is an easy, simple, cheap and safe alternative to using acid. No special equipment is required so it can be done in the home environment. All that is required is an “AA” battery in a battery holder with leads attached, a switch (optional), a two-litre beaker containing 250 g. of copper sulphate made up to a litre with tap water (electrolyte), a small copper plate made ready for etching and clean copper plate or copper mesh to act as a cathode.
Electrolytic Etching and Plating Process
Electrolytic or galvanic etching is an easy, simple, cheap and safe alternative to using acid. No special equipment is required so it can be done in the home environment. All that is required is an “AA” battery in a battery holder with leads attached, a switch (optional), a two-litre beaker containing 250 g. of copper sulphate made up to a litre with tap water (electrolyte), a small copper plate made ready for etching and clean copper plate or copper mesh to act as a cathode.
During electrolytic process the cell becomes a self-sustaining system. Whilst copper is being lost from the anode the same amount of copper is being built up on the cathode. This might create the impression that the copper particles migrate from one plate to the other this is not the case. The copper being lost from the anode combines with the sulphate ions to form new copper sulphate at the same rate that it is losing copper ions at the cathode. The electrolyte maintains its original concentration and can be used indefinitely. The stability of the electrolyte enables bite times to be calculated more accurately than with acids, ferric chloride or saline sulphate etching.
The advantages of electro-etching are:
- No toxic gasses are produced; this eliminates the need for expensive ventilation systems.
- The system is self-sustaining so the electrolyte only requires topping up owing to of evaporation.
- The stability of the system means that biting times can be estimated accurately, unlike when using acid or metal salts such as ferric chloride, saline sulphate or Bordeaux etch which tire over time requiring etch times to be adjusted for an ever weakening mordant.
- Produces a better-drawn line than other mordants.
- Metal can be added to the plate
The problems that relate to the disposal of toxic chemicals are almost eliminated, because as long as the electrolyte is filtered occasionally, it will have an infinite life.
Electrotyping also known as galvanoplasty uses electrolysis to accurately reproduce in metal any object with an irregular surface. If a mould can be made of an object electrotyping can produce an exact facsimile of it. The process was identified by the observation that the cathode electrode of a Daniell cell became coated with a thin film copper from the electrolytic process. When the copper foil was peeled off the cathode it had on its surface a perfect replica of the marks on the surface of the electrode. The process developed from this observation was that if an etched metal plate is connected to the negative pole of a battery making it the cathode electrode the deposition of the copper onto the cathode provides a perfect copy of the plate. It was this observation in 1839 that led to the development of electrometallurgy.
Examples of Electrotyping.
Electroforming uses electrolysis to make a metal copy of an object. A model or mandrel is made of the object to be copied, usually in wax. The mandrel is made conductive by coating it with graphite or conductive paint. It is then placed in a tank containing the electrolyte and connected to the negative output from the rectifier (cathode). An electrode of the metal to be used for deposition is attached the positive output (cathode). As the current flows through the system a layer of metal is deposited on the mandrel. When the metal layer is thick enough to be self-supporting it can be removed from the tank. A wax mandrel can be removed from the cast by making a small hole in it and applying heat to melt the wax.