Etching is the selective removal of metal by chemical action.
The word 'etch' is derived from Dutch and German words meaning 'to eat' or to 'corrode'. In this process, metal objects to be etched are immersed in a solution of chemicals normally acid. The areas not to be etched are entirely covered in a thick sticky resist commonly known as stopping-out varnish, to protect them.
The acid will gradually eat into and corrode only the exposed areas of metal, whilst the protected metal remains intact.
Success in etching lies in the careful control of the etching solution, the application of the resist and the timing of the process, so that the correct depth of etch is achieved.
Etching is normally used in metalsmithing to create a figured, decorated or textured pattern on a surface. Depending on factors such as the complexity of texture desired, the amount of metal to be etched and the depth of etching, decisions are made as to the number of separate etching processes used.
A surface can be constructed in two basic ways:
1: The entire surface is covered with stop-out varnish and gradually scratched back and etched many times, revealing more metal at each stage. Here the first scratches will end up being the deepest lines on the etched surface.
2: The surface is painted with stop-out in limited areas only and etched repeatedly adding more stop-out each time until almost the whole surface is covered. This time the last areas to be covered will be etched the deepest.
Wearing appropriate safety equipment (googles, rubber gloves and plastic apron) is essential as well as doing the etching in a well ventilated area and preferably using a chemical fume extracted cabinet. Concentrated acids are potentially dangerous and great care should be taken while handling these.
Acid should always be added to water when preparing the etching solution and never the other way around.
To etch silver, a 20 per cent solution of ferric nitrate is dissolved into water or 1 part od nitric acid to 5 parts of water.
To etch copper, a 20 per cent solution of ferric nitrate is dissolved into water or a 20 per cent of nitric acid is dissolved into water.
To etch aluminium, a 75 per cent solution of caustic soda is dissolved in water.
To etch steel, 1 part of nitric acid is dissolved into four parts of water.
To etch pewter, 4 to 10 parts of nitric acid are dissolved into 1 part of water.
The object to be etched should be immersed carefully into the etching solution. Shortly afterwards bubbles will appear on the exposed metal surface. To remove them the tray is rocked gently at short intervals. If the bubbles are allowed to remain, the line will not be etched evenly because the gas contained inside the bubbles keeps the acid away from the metal.
The forming of the bubbles is an indicator as to the strength of the acid and the speed of the action. As a general rule weaker solutions tend to etch straight down while stronger ones may have an undercutting reaction and even lift away or alter the resist.
Etched brass earrings.Aimee Addison.