Acid etching is the oldest chemical method of engraving brass and other metals. Its many uses include printed circuit boards, printmaking plates and decorative plaques. You can produce patterns by applying etch-resistant ink before acid engraving. Certain chloric acids provide the engraving bite or 'etch.' After etching, a bath in another acidic solution provides the piece with its coloured patina. Many printmakers and engravers now use electrolytic engraving and laser etching rather than acids because of environmental and health concerns. However, acid colour engraving can be performed quickly, safely and independently, with pleasing results.
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Things you need
- Thin brass plate
- Steel wool
- Chemical resistant, such as laser toner
- Laser printer
- Glossy photo paper
- Clothing iron
- Acid solution etchant
- Corrosion resistant plastic container (acid etch tank)
- Plastic tongs and/or clamps
- Agitation source
- Heat source (optional)
- Chlorine bleach (optional)
- Acid solution colourant, such as cupric nitrate
Clean the brass plate thoroughly by scrubbing it with the steel wool.
Print a negative of the pattern to appear on the brass. Use a laser jet instead of an ink jet printer, and use glossy photograph paper.
Place the paper face down on the brass, and iron the paper flat over the surface.
Apply steady pressure, move the iron slowly over the entire surface in an even pattern. Allow the plate to cool completely before handling.
Peel off the paper, washing it with water if necessary, leaving only the ironed-on pattern from the toner on the brass plate.
Prepare a solution of ferric chloride, or of copper chloride in aqueous hydrochloric acid. These can be obtained at electronics shops, for example, as crystals or already in a solution. Refer to the manufacturer's instructions for dissolving.
Install the agitation source (such as a pump with a plastic hose) with one end of the hose at the bottom of the etch tank. Fill the acid etch tank with enough acid etchant to cover the brass plate.
Immerse the resistant-coated plate into the acid bath, holding it by the tongs or resting the clamp on the edge of the container. Turn on the agitation source so that bubbles rise constantly but gently through the acid bath. Turn on the heating source, such as a spotlight close to the tank, if desired.
Allow the plate to rest in the acid bath as long as it requires the etching to bite into the metal the desired depth. Remove the plate after about five minutes to check the progress, then every two minutes or so after that.
Remove the plate from the bath when the etching reaches its necessary depth.
Thoroughly wash the lingering acid solution and remaining resistant off the plate by rinsing it with water, adding household bleach if necessary. This rinsing will also cool the plate for handling if the acid bath was heated.
Scrub the brass once more to prepare it for patina. Apply selective resist in a new counter-pattern as above, if desired.
Prepare the appropriate colourant solution depending on the colour patina chosen.
For example, to turn brass a basic green colour, prepare a solution of 1 tsp cupric nitrate with 1 litre of distilled water.
Heat the metal and/or the colourant solution as necessary. Apply the solution to the metal by immersion (as with the etchant, but in new containers) or by swabbing as necessary.
Allow the colourant to rest on the metal. Then, remove it and apply fresh solution as neccessary, until the desired colours are reached.
Thoroughly cool and wash the metal plate, as above. Use water and steel wool to burnish the surface of the engraved, coloured brass.
Dispose of all hazardous chemicals and used containers according to local and federal regulations.
Tips and warnings
- The process of etching, or engraving, occurs separately from the process of colouring the brass. Learn the chemistry for each step separately, and experiment carefully and under supervision until the processes feel comfortable and safe before embarking on large-scale or complex productions.
- Use caution when handling acids, especially undiluted acids. Wear all appropriate safety equipment, including long, heavy-duty chemical gloves, goggles, aprons and a respiration mask. Do not inhale fumes, and work in a well-ventilated area.
- The chemicals used for this process pose no major immediate health or environmental risks on their own. However, the waste solutions, such as acids containing dissolved copper, cannot be poured down drains. Dispose of these materials at a local hazardous waste facility.
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