Stainless Steel Fasteners Coloured Converted
Coloured stainless steel fasteners
Colouring of stainless steel fasteners requires the use of a mixture of chromic and sulphuric acids that develop the thickness of the naturally occurring passive film on the steel surface, depending on the immersion time. It is a two-stage immersion process that requires close control over the operation's parameters and a considerable skill to get the required colour consistency.
Colours produced For Fasteners
The colours produced are the result of light wave interference effects, as light is reflected from the surface of the thickened oxide passive layer and interface of the passive layer and steel surface.
The sequence of colours formed as the passive film grows in thickness, colour ranges from bronze, through to blue, black, charcoal, gold, red-violet and green, intermediate colours are difficult but also possible.
The finished thickness of the passive film ranges from 0.02 microns to produce a bronze colour effect to 0.36 microns producing a green colour effect between the passive layer and the steel surface of the sheet.