Master Polish,,Bright Blue,,what ever anyone might call their (re)bluing,,the process of Hot Salt blue is the same.
The preparation of the surface is what makes 95% of the difference in the final look of the job.
Anyone can make the steel look shiny.
But soft edges, rounded corners and even ever so slightly dished out screw counter sinks and factory lettering are the signs of less than quality job.
The polishing job can look like a chrome plated Caddy bumper, the bluing job on that steel will look like deep blue water.
But the 'bluing job' is second rate overall because of the polishing job.
Polishing is one of the most difficult things in gun work to do well and to do well with in a timely manner to make $$ at.
Enter the machine buffers and even machine polishers with hard wheels and belts.
They still take ungodly amts of time to learn how to hand hold the parts and maneuver them across the spinning surfaces to polish them and not cut down corners, destroy lettering and dish out pockets.
Yes hand polishing is always an option. But it'll never do if the aim is to make money and a timely turnaround. It is slow tiresome work and usually set aside for custom and one-off restoration type jobs.
Many hand polished jobs fail to meet the high luster demands of some items.
Machine polishing is sometimes the only way to get that and then the danger of damaging the surface and edges once again is there.
Hand polishing won't do on many restorations because the guns being restored were not hand polished to begin with. They were machine polished by master craftsmen at a belt or hardwheel. To restore that look, you have to do that type of polishing.,,and keep the grit lines running in the orig directions. This latter point is something a lot of custom refinishes seem to like to change. Especially the polishing grit lines on things like bbl's, the sides of Winchester L/A's, the flutes on the revolver cylinder,,ect.
The factorys had people in the polishing rooms doing just that for hours on end, most for their entire career. The polishing wheels and set-ups made and formed, balanced and prepped just for the specific parts they made.
That's hardly an option for the average refinisher that takes in most any make firearm for refinishing. He/she has to still do a 'great job' of polishing,,everyone wants that.
But still do it in short time so as to not be too expensive for the customer and still make a profit for themselves.
Plus be able to handle all the polishing that'll be thrown at you in the different types of guns out there. But with minimum equipment so you don't have to equip a 'polishing room' like a factory which would put you under quickly and still not be enough.
So when someone says they can 'polish & reblue' your pre-27 and make it look just like it did when it left S&W and do it for $400,,,,
They just told you they are going to Restore the metal finish.
I would not expect it for that price in todays world.
Perhaps a nice polish and reblue with some soft edges and lettering,,
but not a restoration and that is what most people seem to think they are going to get.
IMO, S&W's that were blued at the factory in the late 60's, 70's and on were nothing other than Hot Salt Blued.
They look like it, they wear like it and they strip off like it.
I know the official word is that S&W was still using the Carbona Oil bluing process,,but I don't see it.
Perhaps for some special revolvers? Maybe?,,but not the common everyday off the line stuff.
Carbona Blue (American Gas Furnace Co Bluing System) has a very distinctive look to it, as does the earlier OpenHearth-Charcoal Blue.
Hot Salt Blue does also.
DuLite has been around in the US gun industry since the late 1930's.
It's been known how to mix a nitrate bluing solns before that.
Mauser switched to a Hot Salt Bluing mix from Durferrit in the mid 1930's ( Durferrit Co is still around and still makes all kinds of heat treatment salts and compounds).
The process was certainly not an unkn or secret.
It's still the prep and quality of the polishing underneath that is the key.
JMO of course.