etching

Etching is a technique used to remove metal through chemical rather than mechanical processes. Specifically, mordants are used to remove metal by deliberately corroding it. Most often, resists (acid-proof materials) are applied to the metal to control which parts are exposed to the corrosive agent. This allows images (lines, shapes, patterns and textures) to be cut into the metal's surface wherever the bare metal comes in contact with the corrosive agent. Mordants
Mordants are chemicals (usually diluted acids or salts) used to deliberately corrode metal. Since each metal has a different chemistry, different mordants are used depending on what element makes up the majority of that metal's composition. See the metals/mordants chart for more details.
Materials and Equipment
Procedure:
  1. Place your resisted-prepared metal and sample into the prepared mordant bath. Rubber-coated or nylon tongs can be used for this purpose, but it is better to avoid handling your metal with anything that can damage your resist. It is often better to tape nylon string or thread to the back of your piece for taking it in and out of the bath. When using acid mordants such as nitric acid, the piece should be placed face up, because as the metal is dissolved, the reaction produces bubbles that need to be able to escape. When using salt mordants such as ferric chloride, the work should be suspended just beneath the surface of the bath, face down. With this type of mordant, as the metal is dissolved, it produces a precipitate that needs to be able to fall away from the metal surface. An easy way to do this is to tape the piece of metal to a chunk of styrofoam and float it face down on the bath's surface.

  2. After 5-10 minutes, lift the sample metal out of the bath, neutralize it until it stops fizzing, rinse it thoroughly, and test the depth etched so far. Testing the depth is easiest to do by using the tip of a scribe to scratch away the resist at the edge of one of the exposed areas. If there is a noticeable change in depth, you can use this to assess how long to continue etching your piece of metal. Return the sample to the bath.

  3. Continue etching, checking the etched depth at regular intervals. For a cleaner etch, the bubbles that form with acid mordants should be genltly brushed off the metal with a feather. Also, if a mordant is ocasionally agitated (stirred or rocked) the metal will etch cleaner and faster.

  4. When the etch is complete, thoroughly neutralize the pieces of metal and the materials used to handle the metal, and rinse well. Avoid etching for too long, or in too strong a mordant, as this will cause under-cutting. If using ferric chloride, neutralizing and rinsing the metal will not completely stop the reaction. The metal will also have to be scrubbed with an ammonia solution.

  5. Remove the tape, string and foam. Remove the resist with the appropriate solvent, or burn it off with a torch.
Safety:
  1. When mixing mordants, always add acids to water to avoid explosive reactions.
  2. When etching or handling mordants, always wear eye protection, rubber gloves and protective clothing.
  3. Always use acids and ammonia in a well-ventilated area, and have neutralizing agents handy.
  4. Never mix different acids and/or salts together. Never mix ammonia and chlorine

 

Metal
Mordant
Copper-based Metals:
copper, brass, bronze,
NuGold, nickel

fast etch
one part nitric acid and two parts water

slow etch
one part nitric acid and five parts water

clean etch
ferric chloride

 

Silver-based Metals:
fine silver, sterling silver

fast etch
two parts nitric acid and one part water

slow etch
one part nitric acid and three to five parts water

clean etch
ferric nitrate

 

Ferrous Metals:
iron, steel

standard etch
two parts hydrochloric acid and one part water

deep etch
one part nitric acid and one part water

slow etch
one part nitric acid and four to eight parts water

 

Gold and Gold Alloys

Dilute Aqua Regia
one part nitric acid, three parts hydrochloric or sulfuric acid, forty to fifty parts water.

 

Aluminum 1.5 fl.oz. ammonia, 5g copper sulfate, 14 oz. sodium hydroxide, 2 gal. water.