Etching

Etching takes place in liquid ferric chloride. You can etch horizontally in photo trays or vertically in tanks. If you use a photo tray, mix a so called Edinburgh Etch once and for all: Dissolve citric acid powder in warm water and add the 45 - 47 Beaumé degrees ferric chloride. The citric acid ensures a fast and accurate etching and also prevents the ferric chloride from crystalising during the process. This renders it unnecessary to sweep away crystals during the etching - you can simply leave the plate with the art work facing upwards.This etching technique was developed by the printmaker Friedhard Kiekeben in Edinburgh.

Edinburgh Etch - 5 litres for etching in tray
Stir 1/4 litre of citric acid (250 grammes) in 3/4 litre of hot water.

• When the citric acid is dissolved, add 4 litres of liquid ferric chloride 45-47 Beaumé degrees.
• A fresh Edinburgh Etch must be kickstarted - let a piece of copper be eaten up in this mixture before use.
• The mixture is ready for use. Etching must take place in an open tray (no lid). It is recommanded to use a system called "acid tray with rim exhaust". This allows you to do the etching with the cover closed, since there is a ventilation system inside the system. Ferrich chloride is however far less dangerous to health than nitric acid.
• Keep the Edinburgh Etch in the tray under an airtight lid or pour it back into the bottle after use.
• Etching in tank
  Fill the tank with liquid ferric chloride 45-47 Beaumé degrees and do not add citric acid when etching vertically.
• Switch on the aereator in the tank. The bubbles should sizzle only in the surface of the liquid.

Materials
Liquid Ferric Chloride 45-47 Beaumé degrees (72%)
Citric acid powder

Backing the Plate
Before etching the plate must be backed

• Place the plate on a glass plate and cover it with packing tape.
• Trim the edges with a hobby knife.
• Make a plate hanger or handle for lowering or pulling the plate up out of the ferric choloride.

Stopping Out Before and During Etching
If you want to stop out certain areas of the etching ground, before or during the etching process, you can paint on an acrylic stop-out with a brush. The stop-out is jet black. If the plate has been etched before stopping out it has oxydized in the ferric, and you must de-oxidize it before applying the stop-out.

• De-oxidize the copper plate.
• Rinse the plate in running water and dry it for a few minutes in the drying cabinet.
• Brush on the stop-out.
• Harden the plate in the drying cabinet approx. 10 minutes before etching.

De-Oxidizing
If the plate has been etched and you want to apply stop-out or any other etching ground, it must be de-oxidized first.

• Mix 2-3 spoonfuls of fine table salt with 1 litre of vinegar. Stir well. Keep the solution in a bottle or plastic container.
• Place the copper plate in a tray and pour on the solution.
• The plate de-oxidizes immediately. Rinse it in water and dry it. The plate is now ready for the application of the etching ground.
• Pour the solution back into the bottle - you can use it many times. It becomes green when it has lost its effect.

Stripping
Acrylic- and water-based etching grounds can be removed in a mild solution of soda crystals and water. Soda crystals are best dissolved in hot water. Soda is an alkaline product which may irritate the skin. It is therefore preferable to use rubber gloves while stripping the etching grounds.

• Stir 6-10 tablespoons of soda crystals in 2 lites of hot water.
• When the soda has dissolved completely, pour the solution into a photo tray.
• Place the plate in the tray with the etching ground facing up.
• After 5-20 minutes the ground can be washed off under running water.
• Finally remove the packing tape on the back and dry the plate.
• The stripper can be used for several plates before it is finished.

Materials
Soda crystals (soda ash)

(this page has been copied from Henrik Boegh's page, Grafisk Eksperimentarium)