The particular process types to which this code applies are as follows:-
- Etching of metal plates, in particular those made of either magnesium or zinc, with a corrosive fluid which is most often nitric acid.
- Washout of photopolymer plates with an organic chemical as a solvent. The plates may be wholly of photopolymer material and hence flexible (e.g. Cyrel process), or they may have a metal backing with a photopolymer upper layer as the soluble surface (e.g. Nyloprint process).
- Lithographic processes which involve etching with corrosive fluids. It must be pointed out that this does not apply to all lithographic processes, but generally to the so-called 'multi-metal' systems where an upper plate layer of chromium is partially removed by etching to reveal the underlying
copper or brass layer which provides the image. The deep-etch plate process, involving a single metal layer, is a further example of a process in this category.