Etching Resist

The use of UV Activated Emulsion as a Resist for Etching.

Preparing the Metal:

The metal is de-greased as usual, using pumice or scouring powder, so that when wetted water will form a film and not droplets.

A little of the blue emulsion is dispensed onto a glass sheet and using a print maker’s hard rubber roller, applied as thinly as possible to the dry metal plate. The material is not very sensitive and can be handled in a dim dust free area, away from direct daylight.

The coating is then allowed to dry in a closed, light proof box for four or five hours or overnight. A cardboard box with a deep lid works well for this.

 The Image:

A black and white image is printed onto acetate sheet and to ensure that it is opaque enough, three copies are superimposed as accurately as possible, by holding them up to a window or a light box and then taped together at the edges.

Exposure:

The printed acetate is now secured to the coated metal and exposed to UV light.  This can be from a bought UV exposure unit, a homemade unit such as an upturned wooden box, containing a small fluorescent light fitting with UV tubes, or even a nail curing light.

With bought exposure units, the metal and the acetate sheet are kept in close contact against a glass screen, by a pressure pad in the lid. For improvised units a piece of clamped or weighted glass can be used.

As a guide the exposure time is eight to ten minutes depending on the device used. Thick lines require less time and thinner lines more.

The time needed can be verified by trying three or four exposures on a prepared test piece masked with a piece of card, which is moved along at intervals, so that the first area has the longest exposure and the last the shortest.

Developing:

After exposure, the acetate is removed and still in subdued light, the metal sheet is immersed in a solution of soda crystals, using one table spoonful in about 200ml of warm water, which will dissolve that part of the emulsion which was protected from light by the image.  This is helped along by gentle sponging. The light cured resist which remains, will give you a negative of the original image after etching.

The Etchant.

The preferred etchant is ferric chloride for base metals and ferric nitrate for silver. Once etching is complete, the resist is removed by sponging with hot caustic soda solution, using one tablespoonful in 200 ml of very hot water.

Materials

Photo Imageable Etch Resist 200g £25-10, from Intaglio Printmaker, 62 Southwark Bridge Road London

UV Exposure  Units from Maplin and other stores online.

Rubber roller from art supplies or from the above.

Soda crystals (washing soda), Caustic soda (caustic soda drain cleaner) and washing up sponges from hardware shops.

Please note that washing soda and more particularly caustic soda are extremely damaging to skin and eyes, so rubber gloves and eye -protection should be worn.

Acknowledgements.

This method was first described to our tutor by Gordon W. Robertson, Multi-Media Artist and adapted for the class by our tutor Helen Smith at Morley College London.

Dennis.