This SS burnishing is applicable in the optical and military fields as we as in the nuts and bolts sector in general. 

It does not require oiling unless it is specifically requested by the drawing.

The blackening process of stainless steel accessories is required: 
   » for aesthetic reasons, when you wish to get a black coloring 
   » to increase resistance to corrosion. 

Stainless steel burnishing is obtained in suited oxidizing solutions at 120/130°C temperature. 

The thickness of the burnishing layer, formed essentially by oxides, is approximately 0.1 microns; therefore it does not affect the dimensions of the treated details.

Complying with standard MIL-DTL-13924