A clean and passive surface finish is crucial to corrosion resistance. Stainless steel is protected from corrosion by its passive layer - a thin, impervious, invisible, surface layer that is primarily chromium oxide. The oxygen content of the atmosphere or of aerated aqueous solutions is normally sufficient to create and maintain ('self-heal') this passive layer. Unfortunately, surface defects and imperfections introduced during manufacturing or caused by aggressive chemical loadings may drastically disturb this 'self-healing' process and reduce resistance to several types of local corrosion. Thus, as regards hygiene and corrosion, a final cleaning process is required to restore an acceptable surface quality.