To the original question regarding the inconsistent coloring, I would agree with Steve (usually a good idea wink ) that the mill mixed steel of different origin, and not purposefully.

We've discussed pattern staining, and there are links here to threads
https://docs.google.com/document/d/1EGInyr3CsRadXkmTYRak4TWK-pCB3cN5Wgg51u_SnEM/edit

Iron & steel sources
https://docs.google.com/document/d/1V-qkkHrs7yJakMkakxkiMx8FzJjGXUg0EDm8-_AQPiA/edit