Acid etching is an artistic technique to imprint a design onto a surface. Acid etching is often used on glass, metal and stone. Designs are cut from paper and placed on the surface of the object to be etched, which is then covered in a strong acid solution. The acid erodes the surface of the object, creating a different colour and texture than the part of the surface that was protected by the paper. It is dangerous to work with strong acids, so take precautions when performing acid etching.
Create the design you would like etched into the stone by drawing it onto contact paper using a pen or pencil. Use an exacto knife to remove the excess paper from the design. The design shown in the contact paper will retain the current colour of the rock, while the rest of the rock will change colour due to the etching.
Remove the back of the contact paper to expose the adhesive and place it onto the rock.
Work outside in an area with good ventilation to allow the fumes from the acid to escape.
Wear goggles and rubber gloves to protect your skin and eyes from the acid.
Pour hydrochloric acid evenly over the surface of the rock. Hydrochloric acid can be purchased from home improvement stores. Solutions that have been diluted will need to sit on the stone longer than an undiluted acid. You may use a natural bristle brush to sweep acid over delicate areas to ensure even distribution.
Check the level of etching by washing away a portion of the acid with clean water. If the etching is acceptable, wash the entire surface with water.
Allow the rock to dry fully before removing the contact paper.
Hydrochloric acid is a strong acid. Protect your skin and eyes when using and allow for ventilation so that you do not breath in the fumes. If you are working outside, acid poured into the ground can change the pH of the soil. Sprinkle baking soda over spilt acid to neutralise it.