Also known as chemical milling, etching can be used to create master prints or dyes out of metal pieces to be used to create numerous imprints of a design or image.
In the process of etching, material is selectively removed along lines or patterns by using either layers of chemically resistant material or by only partially immersing the part in the acid or etching chemical. Common chemicals used in etching include sodium hydroxide, hydrochloric acid, nitric acid, cupric chloride and more.
The chemical used is determined by the metal being etched as some acids are more effective on certain metals than others. The part to be etched is thoroughly cleaned before the masking layer or resistant material is applied. It is important for good adhesion to occur between the masking layer and the part in order to ensure consistent removal of the masking layer.
This will further ensure uniform etching in the desired pattern. Masking can be in the form of a tape or painted coating which resists the etching chemical and prevents removal of the part in areas where it is not desired. Elastomers such as rubber and neoprene can also be used as masking layers to separate the material from the etching chemicals and allow for the desired part marking.
The pattern or image to be etched is then carved out of the masking, exposing the part to the chemical and allowing the pattern to be etched into it. Careful consideration must be taken with regard to determining the amount of time the etching chemical or reagent is allowed to act upon the part, and this will be dependent on the material being etched.
Etching is commonly used for metals, glass and stone, and the longer an acid is allowed to react with the material for, the deeper the lines etched will be. When the desired depth of etching is achieved on a part, it is thoroughly washed and sent for further machining. Applications such as circuit boards, solar cells and semiconductors are made using the process of etching. It can also be used with larger items such as aircraft components and extruded frames for larger aircraft and missiles.
If it is a print that is being etched, after the resisting layer of masking is cleaned off, the surface of the part is covered in ink and wiped. Ink will remain in the etched pattern or design and when applied to a material such as paper or a soft plastic in a press, will be transferred, creating an imprint of the image. This can be repeated numerous times with consistent results and is an effective method of printing, but it less common today than other types of printers such as industrial inkjet printers.