You may be seeing forging lines in the metal. Dark streaks that appear from that process usually on the earlier made frames. I don't know what the technical term for them is. But they show up on the Winchester L/A and others.


There should be no need to 'degrease' with the alcohol after every carding. It's either clean or it's not when you start.
If you are dragging oil or grease onto the surface by way of a contaminated carding wheel or even some how contaminated application swab,,clean up that situation and leave the clean metal alone.
The more you fiddle with the surfaces you are trying to blue, the more chance there is of introducing something to spoil the bluing.

Another thing to check is the blue soln itself.
LMF is good stuff. But NEVER wet your swab out of the main bottle and NEVER pour any unused soln from a job back into it.
Pour a small amt to be used for a job out into a separate container and work from that.
Any contamination will be kept there and not spread to the entire bottle. Not pouring unused soln back in saves the main bottle from the same fate.

It keeps you from accidently tipping the man bottle over while working with it too and losing most of it on the bench.
A screw cap plastic med bottle works well for keeping the smaller amt.
I still keep the left over from a job in that pill bottle and use it to blue screws and pins if I need too but never for a 'job'. More often I use the Express Blue left over for the small screw and pin stuff anyway.

Check what you are using for an application swab too.
Some fabics have a softner, fresh scent or sizing washed into them and that can blend with the bluing soln as you are applying it and cause streaks.
Even old shirt material that's 'washed out' still has been laundered and that last cleaning means laundry soap of some kind. They all have softeners, scent and pretty stuff in them and that stays in the fabric.
Paper toweling bits can do the same thing.

A small flat plain soft paint brush works well for application. Squeeze out most of the soln so you don't get runs and it goes on nice and even.