An explanation of basic principles of electrolytic etching, electrical units, the advantages over acids: the economy, consistency, safety, and versatility of galv-etch, and the simplicity of the Galv-on method. Extract from GREEN PRINTS by Cedric Green published by Ecotech Design, Sheffield, UK. - a handbook on new methods for non-toxic intaglio etching and metal plate printmaking, featuring the technique of Galv-Etch, a modern development of the 19th century electrolytic technique of Electro-Etching, and introducing Fractint and other new alternative methods avoiding the use of solvents and chemicals harmful to health and to the environment.
In earlier versions I assumed too much basic knowledge of the scientific basis of electrolytic processes, which has led to very many questions, and a few printmakers making some mistakes which would have been avoidable had they understood the principles behind the galv-etch processes more clearly. Skip this section if you know all about electricity and electrolysis.
For many centuries the traditional process used for etching a plate for printing was to use acid, either nitric, hydrochloric, and more recently ferric chloride, which is weaker but still relatively dangerous to use (see Etching zinc Plates). Galv-etch is an electrolytic process, the principles of which have been known since the early 19th century (see Galvanography - brief history), and the original process was described in 1855 and called electro-etching. It is similar to the process that takes place when a wet battery like a car battery is charged, and a reversal of the process that takes place when a battery is discharged. A battery produces a direct current, unlike the mains electrical supply, which is an alternating current. In order to charge a battery, a direct current must be used, and similarly, an electrolytic etching process requires a direct current, which is why the mains supply cannot be used until it has been 'rectified' and reduced in voltage from 230 or 110 volts to very much less, usually not above 12 volts. The equipment to do this is known as a transformer and rectifier, and the most common household examples are the little power supplies that one can get for battery driven transistor radios and other electronic equipment. But these are not sufficiently powerful for electrolytic etching purposes, but another commonly used, off-the-shelf, transformer and rectifier that can be used is a car battery charger. (TOP)
If two metal plates, say of copper, are placed parallel but not touching each other in a conducting solution of the same metal, say of copper sulphate, and they are connected to the terminals of a battery or of a source of direct current like a battery charger, then the current flows from one plate to the other through the solution. A complex process takes place in which the separate positive and negative 'ions' that make up the solution are separated and are attracted to the plate of the opposite polarity. Copper sulphate consists of positive copper ions and negative sulphate ions. Normally they are in equilibrium and they stick together like the positive and negative ends of two bar magnets. The current is actually able to flow because of the ions which give the solution the ability to conduct electricity. The positive copper ions are attracted to the negative copper plate (called the cathode) and the negative sulphate ions are attracted to the positive copper plate (called the anode). The copper ions stick to the cathode (if it is clean enough) and the sulphate ions are attracted to the bare areas of copper of the anode and react with the copper of the surface, 'oxidising' it and therefore corroding it in the same way that an acid would. In fact at the point of contact, the process is exactly the same as being etched by an acid. It is as if an acid is being generated very temporarily right at the point of contact! While copper ions are becoming solid copper on the cathode, an equivalent amount of copper is being removed from the anode, and the copper sulphate is being kept in its original concentration, the copper removed from the anode, combining with the sulphate ions to form new copper sulphate at the same rate that it is losing copper ions at the cathode. There is a common fallacy that copper particles flow from one plate to another, but this is a misleading simplification. (TOP)