Why does my workpiece rust after the bluing process?
This is most likely because the remnants of the bluing agent have not been rinsed off cleanly enough. This causes components of the bluing to crystallise on the surface and form a reddish-brown layer that looks like rust. Make sure that residues of the bluing liquid are completely removed at the beginning and end and that the surface is clean. Repeat the blackening process and wash off the bluing chemical carefully and completely at the end!