Since rust blue is a series of bluing over bluing, why can't I strike the barrels bright except at just not over the engravings/barrel markings and then just blue over the whole barrel including the remnants of the old bluing at the engravings/markings?

Many thanks

Travis

You can. But you have to make your new polish match what the original polish was under the engraving.
Coarse new polishing lines bracketing an old marking or area of engraving are a giveaway of that technique when not done right.

Plus you have to figure in what the new polished surfacse will look like after your rust bluing (any matting effect). They have to again match what is under those untouched areas of engraving and markings.
Otherwise the engraved area will show as different. Sometimes not by much,,sometimes a lot.

The old surface no matter how pristine it may appear is usually loaded with tiny marks from handling. They don't show until side by side with a really pristine new surface.

It's something that is done in restoration work quite often so it's not anything that unusual. But it takes some skill to really make it look just right in most instances.

If just rust bluing over an old previous rust blue,,it really helps to break the surface of that old blue with a light polishing with something like 400 or even a scotchbrite pad.
You are not even trying to remove all of the old blue, just cut the surface of that old finish, removing any old dried oil usually in the pores of the matted finish and bringing a clean surface for your bluing to eat in to.
You shouldn't have to scuff the old color much beyond a light blue grey if the finish is still pretty good.
The really thin color/finish spots will catch up in color after a couple coats and any new polished areas from dent removal, ect there after.
Saves a lot of extra polishing sometimes.
The key is matching the underlying polish so everything looks the same when done..

I polish around and up to engraving when doing my metal prep and just scuff over the lettering on my final pass or two with 400 grit to give an even polish. Pretty much what Kutter said. It does take a bit of practice

Awesome feedback.

I am assuming you treat top of rib textures/lines/etc about the same way.

Thanks to both

A fine wire wheel in a dremmel works good on the wavy rib pattern. I rarely touch a patterned rib with paper for more than a quick scuff.

A wire wheel I have mounted on one side of a bench grinder gets the call to take a couple passes up and down the rib to scuff them up and clear anything stuck in there.

On a straight line cut matting like on a Nitro Special the matting can often show scrapes & scratches across the lines from handling. You can carefully retrace each line with a 1/2rd file that is shaped to a fine point (don't know the name for them).
It'll ride nicely in each row and with a bit of work you can elliminate the damage and it greatly improves the looks. It doesn't take all that much time either. Who would bother on a N/Spl and others like that?,,I would as long as I'm bothering to make something of it.

A single point carbide checkering tool can work too,,but I don't like wearing out those expensive tools. The file is actually narrower at the point than a 90* chk'rg tool and works better IMO.
A quick pass when done over the top of the rib with a piece of 320 backed up to remove any burrs and then a pass on the wire wheel blends the work in nicely ready for bluing.

Many thanks

I am not too far off from my first attempt at rust bluing a barrel and other parts.

I am going to either have the nicest nitro special around or the most expensive turd in the bowl. Better to learn on this than the 20 ga ideal grade LC with straight stock I am jonesen to mess. I have resisted so far.

Either way I am learning a lot and can't thank you enough for your thoughts