I have just started slow rust blue project on my Finnwolf and have noticed that after two passes the receiver is a distincly different the colour to the rest of the steel.
Has anyone else tried rust bluing and Finnwolf and had this problem and if so what is the fix for it?

Cheers

The barrels are your basic buzzard grade 4140 and they turn black in caustic and soft blue black with Belgium blue. The receivers are chrome vanadium steel. When rust blued they turn a blue color like a potassium niter blue and sometimes with a silver brush color. When you caustic blue them they turn a lovely praple color. Praple is a color. My niece says so ! ! ! !