Some clarifications & answers to questions,,
When I rust blue w/LM, I boil and card after each rusting cycle.
I know some folks that apply the soln,,let it rust. Then card the rust down and at that point with a browned finish simply apply another coat of soln as if they are seeking a browned finish instead of a blued finish.
They only boil the part every other or every 3rd cycle for example before that cycles carding. Some only boil once,,after the last rusting and then the final carding..
I've always rust blued by boiling and then carding each rusting cycle.
Try different approaches. The intermediate, once in a while boiling
certainly saves time.
It may work for you,,it may not. You won't know till you try as there are so many variables in your set-up (water, humidity, temp, soln, techniques, type of steel, ect) that someone else might get great results and you may get miserable results doing what seems like the same thing.
Maybe it'll give you a certain look you are after for the project or style of M/L you're making. It may not be a pristine Holland & Holland look but rather a more muted look and it may unfold right before your eyes with a technique you find that works.
As for the Quick Rust Blue coating. I apply that one last coating just as Quick Rust is normally done.
With the metal warm, a thin coating in applied in long even strokes to the metal with a dampened patch.
Try not to overlap nor scrub the parts with the stuff. Just an even once over covering.
The soln should dry immediately and form a dark gray or reddish colored coating immediately.
Then w/o waiting, take the parts and place them back into the boiling water for 10min or so.
Take them out and that thin coating is now a black oxide coating than can be carded.
Now you are done.
The entire part can be done with the hot rust method of course,,it can be a little more prone to streaking and odd colors if you're not use to working with it. I use it a lot on small parts yet but not so much for bbls anymore.
Hope this helps.