Stripping | The safest stripping system | Making up the sodium carbonate solution | Finishing touches | Straining and disposal
The mordant resists used in etching always have to be able to do two things; they must be resistant to corrosive action but they must also be easily removed after etching has taken place. In traditional etching, the reclaiming stage invariably involves the use of volatile organic solvents, the dangers of which have been outlined. In acrylic resist etching, however, the stripping stage is very different. It is founded on the simple fact that acrylic substances although highly etch resistant, break down easily in an alkaline stripping medium. Many of the traditional problems simply do not arise; the workshop atmosphere is kept free from damaging fumes, no rags are needed, and spent stripping solution can be discarded safely and easily. Nevertheless, as with all chemicals, some basic safety precautions should be followed.
The safest stripping system
A wide range of alkalines can be used for stripping acrylic grounds. The exact mixtures very much depend on the kind of
acrylic resists that need to be removed, and ultimately, each artist/ workshop/ educational institute should employ a stripping method or methods best suited to their specific requirements. Possible stripping alkalines range from agents such as Ajax domestic cleaner and ordinary washing soda through to the very powerful but corrosive caustic soda, the use of which is generally not recommended (it can burn human tissue) unless used with the strictest precautions.
Where a safe and foolproof method is paramount – this applies particularly to workshops used by beginners or for artists practising acrylic resist etching in their private studios in a more makeshift environment – the following system is best. The main ingredient of the safest stripping solution is commonly known as washing soda or soda crystals. Its chemical name is sodium carbonate. Small quantities of this inexpensive alkaline are often used for domestic purposes such as unblocking drains, and can be obtained from most hardware stores or supermarkets. Larger supplies can be ordered from local chemical wholesalers. Once the sodium carbonate has been dissolved in water it can be used to fill a tray or tank where it provides a good stripping solution for any kind of acrylic ground. A plate covered with hardened aquatint, stop-out varnish, hard or soft ground, or photopolymer film is immersed in the alkaline bath and left to soak. Most plates will be broken down in a matter of minutes, whilst thicker deposits of resist may require slightly longer immersions in a hot solution for up to 15-20 minutes.
A slight limitation with the sodium carbonate stripper lies only with the fact that it is somewhat less effective on strong acrylic binders such as Plextol as used in the extra strong stop-out varnish; or on multiple layers of acrylics that have been allowed to cure for long periods of time. In rare cases plates have to be immersed for up to an hour or more to reclaim the bare metal surface.
Making up the sodium carbonate solution
MATERIALS
Products and equipment needed to make the stripping solution:
sodium carbonate crystals – kept in an airtight plastic container to prevent the absorption of moisture dust mask, goggles, gloves – wear when handling soda crystals which can give off a fine dust that can be a mild irritant warm water tray/stripping sink
METHOD
Mix the stripping solution as follows:
1. Mix the soda crystals into warm water at a ratio of about 2 parts water to 1 part soda crystals. Remember it is good practice to wear protective gear when mixing solutions. The solution can occasionally be refreshed by adding more crystals. Use the solution while it is still warm as it will be more effective.
2. Place the plate in the stripping solution.
3. Once the plate has been immersed in the stripping solution for a while, carefully take it out of the bath, allowing excess liquid to drain off.
4. Rinse the plate with cold water in a stripping sink. At this stage the jet of cold water should simply remove any leftover particles of liquid hard ground or photopolymer film.
5. Thick layers of acrylic ground may require gentle scouring using Ajax and a soft brush before being rinsed with hot water. This usually removes the last traces of acrylic but in exceptionally stubborn cases, plates can be returned to the stripping solution to soak a little longer.
6. Once the eroded metal surface has fully emerged, squeegee all excess water off and place the plate in a drying cabinet or blot with paper towels. After having come into contact with a variety of chemicals plates often display a certain degree of tarnishing at this stage. This can be particularly true of zinc and aluminum plates which should not be left in the alkaline stripping solution for very long periods.
Finishing touches
Prior to printing, plates can benefit from being lightly polished with a rag containing some metal polish like Brasso as this brings out all the bitten detail, and in the case of sanded plates even removes the faint surface texture. Fine steel wool, emery paper or fine grit sandpaper can also be used.
Straining and disposal
If a lot of stripping is carried out, a substantial build up of floating acrylic residue is likely. This should be kept out of the drain both for environmental reasons and to prevent blockages. A simple straining devise (such as is used in kitchen sinks) will collect the waste which can then be removed at regular intervals and disposed of. More elaborate straining systems can be incorporated in the sink design of professional workshops.