I dont know if this is helpful but ... I did a slide for a 1911 in Mark Lee's express blue which while not difficult .. was not express. What I got was a very black black. This was soon after I finished and it remained black but I could never figure out how to get that depth you see in some of those awesome old smiths. Cant explain it but I am sure you know what I mean .. the bluing that looks so deep its under glass. I may have not done something properly after I did the bluing but I did get a nice even black.