Leighton,

I'm not sure... I have been doing a few rusts between etchings to have a strong color before dipping in the ferric chloride. I can manipulate the color better this way than dipping after every rust.
Although, the rifle barrels I'm doing now seem to respond better to dipping every time?... I try to have a set sequence to get the same color everytime, but it never works out that way!