Acrylic Resist Etching
It is a well established fact that the conventional materials for intaglio printmaking contain quite a cocktail of acids and chemicals, the danger of which is unmatched in the creative arts. Each of them may have damaging effects on the health of the artists and on the surrounding environment, but in combination they pose a very serious threat to anyone who uses them with some frequency.
(Henrik Boegh – Handbook of Non – Toxic Intaglio)
By using acrylic resists – which use water as solvents, water based inks and vegetable oil and washing soda as cleaners together with ferric chloride (a salt) instead of nitric or sulphuric acid these toxins can be avoided and the health and safety of the printmaker and the environment can be assured.
Bevel Edges, round off corners and de-burr.
This is done for a number of reasons. It protects the press blankets from possible tearing, allows the acrylic ground to flow around the edge and is a safety precaution to avoid cutting hands.
It is vital that the plate be thoroughly de-greased to allow the acrylic resist to adhere properly –.
1. Sand with fine wet & dry sandpaper or fine carborundum paste (220 grit Carborundum + a little water) – rinse
2. De-grease with a few drops of soy sauce (a paste with whiting powder and soy also works well)
Liquid Hard Ground
At Wharepuke we have developed our own liquid hard ground in collaboration with Gerald Ferstman from the University of Kentucky (USA).
The resist is based on Liquitex Pouring Medium and a commercial acrylic floor polish.
To make 1 litre:
60 ml floor polish
30 ml Liquitex Pouring Medium
10 ml water
An article outlining the research was published in the Spanish based printmaking journal Grabado y Edition No.38 (April 2013) and can be seen here The Search for a Worldwide Acrylic Hard Resist Grabado
N.B Do not shake the bottle as this produces bubbles which stop the ground applying evenly.
1. Hold the plate above a tray and pour on a liberal amount of resist in one go.
2. Distribute it quickly before it has time to dry and place vertically on newspaper to allow run off of excess.
3. Move the plate a few times to avoid a build up along one edge.
4. Leave to dry – when touch dry put the plate in a drying cupboard or use hairdryer (approx 10 mins) – the heat strengthens the co-polymer.
5. If you prefer a black surface to work on paint poster paint over the plate and allow to dry. This must be removed in warm water and detergent before being etched so it doesn’t ruin the ferric chloride.
Copper etching allows for very accurate fine lines and cross hatching to be employed without foul biting.
Backing the Plate
Before etching the back of the plate needs to be protected.
1. Cover the back with packing tape.
2. Trim edges.
3. Make a handle for lowering in and out of ferric chloride, you may wish to initial this to keep track of your plate
Etching takes place in liquid ferric chloride using the Edinburgh Etch, a mixture of Ferric Chloride and citric acid in an aerated vertical etching tank or open tray.
For 5 litres:
Dissolve 250g citric acid in warm water add cold water to make 1 litre (750ml). Add to 4 litres Ferric Chloride – use this ratio to calculate all other amounts
1. Place the plate face up in the tray of ferric chloride or hang by tape handle in the etching tank
2. Make a note of the time the plate went in.
3. The timing depends on a number of factors – the age and strength of the ferric chloride and the temperature can affect the speed of the etch. If the mixture is used infrequently it may be necessary to kick start it by putting in a scrap of copper 3-4 hours before using. As printing can take place without removing the ground you can always print at intervals until the desired depth is reached. An etching could be achieved from anything from a half to two hours.
Acrylic grounds can be removed in a mild solution of soda crystals or soda ash. 5 tablespoons per litre of water – This also removes any excess tape from the back of the plate.
At Wharepuke we use Akua water based etching inks.
1. Apply ink to the whole plate with a piece of card.
2. Remove excess ink with card.
3. Wipe with newsprint (old telephone books) – wipe edges with rag and clean any excess ink on back of plate
4. Print on dampened paper – time of soaking depends on type of paper.
Etching Aluminium, (Zinc & Steel)
The Saline Sulphate Etch
Aluminium, zinc and steel are etched in a solution of copper sulphate, salt and water.
In etching, aquatint is normally used to fill open areas on the plate with durable tones or a black. The Saline Sulphate etch for aluminium is self aquatinting. During etching a very distinctive and durable surface roughness occurs in the open areas, this crystalline texture can produce a beautiful black on the print all by itself. As a result, there is no such thing as ‘open bite’ in this process since all etched areas become carriers for etching ink, thus enhancing the graphic potential of the process.
Unusually, neither of the basic components of the Saline Sulphate Etch, i.e. copper sulphate and salt, have any corrosive effect on Aluminium by themselves. But etching becomes possible when both substances act on the metal in combination. While all other metals easily erode as long as they are grease free, the surface of aluminium plates is best treated with fine wire wool or carborundum to make the surface more susceptible to the etching process. This should be done before any acrylic grounds are applied to the plate.
The Saline Sulphate Etch involves the production of a loose coppery sediment which floats to the surface and should be removed regularly. However, the continuous rising of small hydrogen bubbles also indicates that etching is in progress (these are not considered a hazard).
Tip: When stripping acrylics off an etched aluminium plate, ensure that plates are not left in the soda ash stripping solution too long as this will etch the plate further.
1. File edges and corners of plate to ensure they don’t cut the press blankets. This also helps the acrylic resist to coat the edges, makes wiping easier and gives a good plate mark to the print.
2. Lightly sand or polish plate surface with wire wool, wet & dry sandpaper or carborundum. De- Grease with soy sauce/whiting powder.
3. Apply 1st coat of Acrylic Resist and let dry.
Apply 2nd coat.
4. Draw image through resist – surface may be painted with poster paint to allow easier viewing of image if desired. Remove the paint before etching.
5. Back plate with packing tape
6. Etch in copper sulphate/salt mordant
7. Remove tape. Strip ground in soda ash solution. (don’t leave too long in soda ash as this will continue to etch the plate). Ink and print
1. Prepare plate as above – file, sand, de-grease
2. Paint or draw the image onto plate using melted vegetable fat (e.g Kremelta) – allow to harden.
3. Apply grounds as above.
4. When dry immerse plate in warm water – fat melts and lifts ground from plate, or simply rub with a soft cloth.
5. Back plate with tape and etch. The image drawn with the fat will be etched into the plate.
1. Make image with sand or carborundum powder and glue on a piece of card and allow to dry.
2. Prepare plate with hard ground as above.
3. Place cardboard plate face down on prepared aluminium plate and run through the press. The sand/carborundum image is punctured through the hard ground.
Recycling, Neutralization, and Disposal
The process comes full circle. The very action that makes the Saline Sulphate etch work so wonderfully as an etching bath – the depletion of copper ions – also facilitates its recycling. N.B – Concentrated copper ions are regarded as an aquatic pollutant and must not be allowed to get into waste water. As more and more copper ions react with the metal plate during etching these are converted into their inert cousins: solid copper atoms. If a sufficient quantity of metal is etched eventually all copper ions are removed. A fully depleted bath is recognized by two features: (i) the solution no longer corrodes metal and (ii) is no longer green but clear and transparent.
A spent etching bath can be made ready for recycling in the following manner:
1) Add hot water to the bath to re-dissolve any solid sulphate particles and stir.
2) Add a pile of metal off-cuts – zinc, steel, or aluminium – to the etching tray.
3) Leave to act overnight.
4) On the following day, drain off the liquid into a bucket and add sodium carbonate (about two or three cups per bucket).
5) Once fizzing stops, the liquid can be discarded.
6) The remaining solids can now be left to dry out, kept in labelled sealed containers and then treated as dry waste.
Although Copper Sulphate is a comparatively safe chemical for etching it is considered a marine pollutant, and if present in rivers or lakes it can kill fish. Therefore it is crucial that solutions containing this salt are never poured down a drain without following the above instructions. Only a spent solution that is lacking the green colour (thus indicating the presence of copper ions) and that has been neutralized with sodium carbonate is safe to be discarded.