Stainless steels coloured by INOX-SPECTRAL-Process. To get good colouring results the alloy has to have a minimum content of 50% iron and 17% of chromium. On stainless steel with a chromium content between 13 and 17% only a reduced range of colours can be achieved, predominantly brown and grey. There are limitations in maximum content of other alloy components. Best results are obtained on austenitic stainless steels. 

Relatively high standards are set with regard to homogeneity of structure and alloy concerning the surface quality of the material to be coloured. Only first quality material provides uniformly coloured surfaces.

On austenitic and ferritic stainless steels with a chromium content of at least 17% the following colours can be achieved:Bronze, cobalt-blue, steel-blue, gold, champagne, red, green, anthracite and black.

Due to the mechanism of lightwave interference which generates the colours, stainless steel surface especially when coloured red and green show changes in colour depending on the angle under which they are looked at. This effect should be taken into account for actual application. Proven standardised colours are bronze, cobalt-blue, gold and black.

Chemical and electrochemical processes of surface treatment like pickling, etching and electropolishing which affect the surface of stainless steel will destroy the coloured surface. Therefore these processes can be used for application of letters and patterns into coloured stainless steel. For that purpose the areas in which the coloured surface is to be preserved are masked by an acid-resistant resist (photoresist, screen-printing or offset printing resist) and subsequently the areas not so prepared are discoloured.