what is galv-etch ?

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)

the electrolytic process

 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)

advantages of galv-etch over acids

  1. The greatest advantage is that with the same equipment, plates can be either bitten down or built up to give a much richer variety of results, and that qualities of tone and texture can be produced that are not possible with acids. In addition, new plates can be created by 'electrotyping' from moulds or from relief created on silvered copper plates - the original meaning of the word galvanography.

  2. Working with copper plates the chemical - copper sulphate - is absolutely safe to use, but gloves should be worn to protect the skin. With zinc plates the electrolyte - zinc sulphate - is much safer than acids, but must be used with care, avoiding contact with skin or eyes, and storing it safely out of reach of children.

  3. For steel plates galv-etch is the safest method, although Bordeaux Etch can be used as a mordant (see section on Bordeaux Etch later). The electrolytes for steel - ferrous sulphate or ammonium ferrous sulphate - are classified as safe chemicals, but I find it prudent to wear gloves where there is any danger of skin contact.

  4. The solutions are not weakened by use, in fact, the same solutions can be used for years and eventually pose no serious disposal problems (see section on safety precautions and Bordeaux Etch for method of disposal).

  5. No gases or fumes are generated nor is there any precipitate or deposit formed in the bite, provided that the chemicals that are used are pure, do not contain salt (sodium chloride) and the metal plate and cathode are the same as the metal in the electrolyte.(see links for dangers of etching with brine).

  6. The length of time taken for a given depth of bite on the same size and type of plate, under the same conditions of voltage and current, is always the same, and the biting can be controlled by time-switch, leaving one free to get on with other things.

  7. Another advantage is that the backs of plates do not need protecting - the strength of the electrolytic action is proportional to the distance between the electrodes, so only the edges and a narrow strip around the edge at the back need be varnished. The semi-dry method leaves the backs of plates completely untouched.

  8. The long-term cost is much lower as no very special expensive equipment is needed, especially with the semi-dry method, and the amount of electricity used is negligible - about as much as a light bulb. There is no danger from electric shock, because both voltage and current are low ( 0.5 to 8 volts at 0.5 to 10 amps).

  9. The electrolytic action is not like the corrosive action produced by an acid, and so the range of varnishes, resists and grounds that are effective is much greater, because they must be simply electrically insulating and not acid resistant. Some heat-sensitive grounds require a low current and cool electrolyte, because galv-etch generates a little heat at the point where the etch acts.

  10. The electrolytic action between the plate (anode) and the cathode is directional at right angles to the face, and so the edge of a resist is not significantly eroded or undercut.

  11. The Galv-On semi-dry method of galv-etching simplifies the equipment required and allows one to work on only a portion of a large plate at a time, and can produce a great variety of textures, tones and images quickly with relative ease. (TOP)

up "Fleurs imaginaires" - plates galv-etched with open bite areas, proofed intaglio and overprinted in relief from the same plate in 2 colours.


©Cedric Green : updated May 14, 2015