Acid etching is used both in industrial applications and by artists to create detailed designs on metal or glass. A strong acid is used to cut the metal, leaving behind a detailed picture. There are two general methods used to engrave metal with acid: metal acid etching and relief acid etching. With artistic metal acid etching, a wax-like form, referred to as a "ground," is created by the artist and dipped in acid. This form is laid upon the metal, producing the design. With relief acid etching, the wax-like form is laid over the metal, and the entire piece of metal is dipped in acid. The relief results in the created design.
Things You'll Need
Hydrogen chloride, nitric acid, sodium hydroxide or iron chloride
Clean the metal by stripping it of all oils and chemicals. Use an alkaline cleanser to remove any organic impurities, and an acid cleanser to remove any chemical residue.
Apply a mask, or "ground," to the entire surface of the metal, for relief acid engraving. Typical grounds are wax-like elastomers (rubber) or plastics, paints or tape.
Cut a design into the ground where the metal will be cut. Remove the mask areas where you want the metal to be etched. Apply the chemical acid to the areas that you want etched. This results in a relief cut. In the case of an etched cut, the ground itself is the design, which you dip into the acid, then lay on top of the metal, resulting in a cut replicated in the ground itself.
Different types of metal require different kinds of acid. For steel, hydrogen chloride or nitric acid works best. Aluminum uses sodium hydroxide. For stainless steel and copper, iron chloride or nitric acid works well.
Strip the acid from the metal after the etch has been created. Clean and polish the metal, burnishing any irregularities in the etch to achieve a uniform effect.
There are a number of factors that will determine how long the acid should remain before being cleaned off of the metal, including the temperature, agitation and concentration of the mixture, as well as the type of cut desired.
Acid concentrations should be weak, rather than strong, because a strong concentration can scratch or otherwise damage the metal.