Making up the Edinburgh Etch
Refer to the INTAGLIO MANUAL for detailed instructions on PLATE PREPARATION, ETCHING THE PLATE and more.
Products and equipment needed to make up the Edinburgh Etch:
- supply of hot water
- ferric chloride solution (purchase ready-made up)
- anhydrous citric acid powder
- heavy-duty gloves
- measuring jug
- buckets for mixing the solutions
- implement for stirring solutions
- tray, bucket or dip tank
(Above) Howard Pro-Vertical Etching Tank: designed by Keith Howard.
See www.danielsmith.com for details.
Make up the Edinburgh Etch as follows:
The Edinburgh Etch solution consists of five parts.
Four parts are a saturated ferric chloride solution.
One part is a citric acid solution.
4 parts ferric chloride solution + 1 part citric acid solution = Edinburgh Etch
4 liters ferric chloride solution + 1 liter hot water mixed with 300ml citric acid powder (ratio 3:1) = Edinburgh Etch
- Put on goggles and gloves.
- Start by measuring out 4 liters* (or the desired quantity) of the saturated ferric chloride solution into a bucket.
- Now make up the citric acid solution using the ratio of 3 parts water to 1 part powder. Fill a bucket with 1 liter* of hot water. Gradually add 300ml* of citric acid powder. Stir continuously.
- When the citric acid powder has completely dissolved, gradually pour this citric acid solution into the ferric chloride solution. Keep stirring until you have produced a uniform liquid. This solution is the Edinburgh Etch.
- Pour your Edinburgh Etch mixture into an etching tank, tray, or bucket.
- The Edinburgh Etch can be used straight away but it is better to run the aeration pump for a few hours first to obtain a perfectly uniform mix.
*These are sample quantities: use less or more according to the ratios provided.
(Left) Ferric Pump: The exemplary etching facility at Western Michigan University includes a large etching tank filled with Edinburgh Etch which uses a professional pump system rather than a fish tank air pump. It provides excellent agitation of the solution and is easy to maintain. The polypropylene tanks have tight fitting lids so that etching can take place in a sealed environment with the minimum emission of corrosive vapors.
The Edinburgh Etch mixture is a universal mordant that can be used in flat trays and upright tanks.
Temperature: The Edinburgh Etch works best in warm conditions (from 18 to 30 degrees C).
A warmer temperature improves etching times and the responsiveness of the mordant.
During etching Edinburgh Etch trays or tanks should be covered with a lid to prevent evaporation. When not in use, etching solutions should be stored in clearly labeled containers, stating the composition of the solution and the kind of metal etched in it. It is also good practice to place safety notices, such as CORROSIVE - WEAR EYE PROTECTION to all containers and work areas.
If no citric acid is available a saturated ferric chloride solution will do the job, but the etch will be slower and somewhat less precise.
Edinburgh Etch for Brass Brass is a superbly suitable material for intaglio etching and printing.
The Edinburgh Etch method allows this noble metal amalgam to be etched as easily as a sheet of copper. Brass can be etched in the same solution as the one described for the Edinburgh Etch for copper.
See the section on METALS in the INTAGLIO MANUAL for more about the suitability of Brass for printmaking.
made using ferric based dye
The strength of an Edinburgh Etch or ferric chloride solution can be tested by dipping a paper strip in the bath. A bright orange color indicates a fresh solution. If the solution is the color of black olives this indicates that the solution is exhausted and requires disposal and replacement.
Testing Freshness: Color CodeThe Edinburgh Etch solution is exceptionally long lasting; a single tank-full, used daily and occasionally topped up to compensate for loss, has been known to remain active for several years without significant drop in its biting properties.
The freshness of the bath can be easily tested: dip a strip of white paper into the bath to assess its color: due to its dominantly iron-based content, a fresh Edinburgh Etch solution has a bright orange or rusty color. A used solution turns green as cupric compounds accumulate in the bath; eventually the solution acquires a dark black/green olive color and a thicker consistency; it is then near exhaustion and requires disposal and replacement.
BRIGHT ORANGE Solution is FRESH
BLUE/GREEN Solution is still GOOD
DARK GREEN / BLACK Solution should be REPLACED
Neutralization and Disposal
An Edinburgh Etch solution can remain active for several years. The citric acid component in the solution allows for literally dozens of kilograms of metal to be dissolved without causing any precipitation. The bound, chelated copper compounds in the solution are considered a much lower hazard to aquatic life than pure copper ions, but precautions should be taken not to allow a concentrated solution to go down the drain. Once the Edinburgh Etch solution is of an oily consistency and of a black olive color, its ability to etch suddenly drops; and it is time for replacement. A simple gravity-fed siphon pump is ideal for transferring the solution from the tank into plastic storage containers.
The ideal way to dispose of spent etching solutions is to take them to a chemical disposal company, such as the ones dealing with waste photo-chemicals or ceramics waste. If a ferric chloride or Edinburgh Etch solution has been properly neutralized with a suitable agent such as sodium carbonate and highly diluted, disposal in the drain may be permissible by some authorities. However, copper ion concentrations in water should normally not exceed about 1 part per million. The Edinburgh Etch contains chelated, non-reactive, copper ions so a higher ratio may be permissible.
To neutralize an Edinburgh Etch or ferric chloride solution, gradually add a strong sodium carbonate solution to it. In a harmless fizzing reaction, carbon dioxide is produced. Allow this to settle before adding more sodium carbonate. Once the solution no longer fizzes when soda ash is added, and neutralization is complete. This can be confirmed by a pH test showing a value of seven. After that, dilute with plenty of water.
A professional etching facility should also have a catchment tank filled with an alkaline neutralizing agent. Manufacturers can provide this ready built into an acid unit.
The Small Business section of your local Environmental Protection Agency offers free advice on the safe disposal of exhausted metal salts and liquid ferric-based etching solutions.
A Guide to the Safe Use of the Metal Salt Etching System
The Metal Salt Etching system is safe to use if the warm and the cold colored metals are etched in their respective warm and cold colored solutions.
Use the rust/orange colored Edinburgh Etch (ferric based) for etching the reddish metals: copper or brass.
Use the blue/green colored Saline Sulfate Etch (copper sulfate based) for etching the silvery metals: mild steel, zinc, and aluminum. See ETCH ZINC, STEEL, ALUMINUM.DO NOT use the Edinburgh Etch or a ferric bath to etch zinc or aluminum, as this may cause a hazardous chemical reaction.
It is recommended that print studios using metal salt etching systems display a notice such as the one below.
NOTE: Although considerably safer, the new systems still utilize harmful corrosive chemicals and their reactive properties, and it is very important to follow all safety instructions in their use. Medical science suggests that as an extra precaution women should not engage in extensive etching practice of any kind (acid or salt based) during pregnancy to safeguard against the possibility of reproductive damage.
Metal Salt Etching Safety Precautions. Strong long sleeved gloves, goggles, and protective clothing (e.g. plastic lab apron) should be worn when handling metal salts and metal salt solutions. Use a dust mask when handling copper sulfate or etching residues. In professional shops ideally there should be an emergency shower and eyewash fountain in the etching space, in an artists personal studio make sure you have clean running water or an eye wash bottle nearby to use in case of splashes. Any splashes in the eyes must be rinsed immediately with plenty of water. Immediately wash off any splashes on skin. Provide supplies of sodium carbonate for neutralizing any accidental spills and run-offs in the etching space. Frequently clean the etching spaces with warm water and mild detergent to prevent build up of salt residues. Keep all solutions and etching residues in closed containers, and keep etching supplies in locked non-metal containers and cabinets.
| METAL SALT ETCHING|
Copper and Brass: Etch in Edinburgh Etch
Zinc, Steel, Aluminum: Etch in Saline Sulfate Etch
DO NOT MIX WARM AND COLD COLORED SOLUTIONS AND METALS