I'm going to lay something out here for your consideration, Vadi:
I know a bunch of the members of the American Custom Gunmaker's Guild. Very, very, very few of them use hot salt blueing. I think I can recall only one, as a matter of fact. Most all of them are using rust or express blue methods on their fine shotguns or rifles. I'm talking of guns that go for $8,000 and up. As I mentioned up-thread, as soon as you start doing some of the high-end features on custom rifles (sweated-on sights, soldered-on quarter ribs on rifles, or ribbed double guns), you can't do hot salt blueing. No way, no how.
The only upside to hot salt blueing is the speed with which you can push a bunch of guns through the process. For a commercial blueing shop, sure, this is the way to go. For a guy just starting out and learning? It's a huge hassle you don't need in order to learn how to polish and blue.
If you really would like to find out what blueing is like without investing thousands of dollars, a truckload of permitting and red tape, go get one or two of the smaller gun tanks from Brownells. Here's the URL to them:
http://www.brownells.com/.aspx/pid=1062/Product/BLACK-IRON-BLUING-TANK
If you should choose to go forward with hot salt blueing, this tank can be used to hold hot salts (or anything else, for that matter).
If you get two of these tanks, you could use one for the boiling water in rust blueing to turn red rust black, and you would/could use the second tank to run a solution of Dicro-clean #909 or washing soda.
Put one or the two tank(s) across two burners on your kitchen stove. Fill with water, turn on the burners and get the water up to a slow boil. If the Mrs. doesn't want this going on in the kitchen, get a propane-fired camp stove with two or three burners and a 15lb jug of propane. All you need to do is get some clean water to a slow boil. Same deal with the Dicro-clean: It just has to do a slow boil. You could use the same tank for the cleaning dip as for the hot water. Once you put the guns to be blued into the Dicro-clean and then take them out, put the guns somewhere where they won't get dirty or touched. If you have to pick up the guns after they've been in the Dicro-clean, get some cotton gloves. Use them ONLY for handling the cleaned steel.
Rinse out the tank, fill with clean water and re-boil.
Now, let's do some rust blueing. Here's one solution I've used, available from Brownells:
http://www.brownells.com/.aspx/pid=22820/Product/CLASSIC-RUST-BLUE
Pilkington's, Belgian Blue, etc all work OK too. If you get a copy of "Firearm Blueing and Browning" by R.H. Angier, you can learn how to mix your own rust blueing solutions from a couple acids and a handful of clean iron nails or filings.
http://www.stackpolebooks.com/produ...0811703260&title=firearm-blueing-and-browning
You just put the cleaned gun into the boiling water, leave it there a couple minutes, take it out. Apply a single coat of the blue chemical with a cotton swab or a cleaning patch held in a pair of hemostats or other method where you don't have to touch the chemical. Paint the solution onto the gun with no drips, runs or sags, getting it as even as possible. I wear disposable nitrile gloves while I'm blueing to prevent getting oils on the steel and acid blueing solution on me.
If you live somewhere where it is humid (> 50% RH), you can just let the gun now sit for awhile. You're waiting for it to grow "fuzz." Don't let it sit too long (eg, overnight), otherwise the chemical will etch the steel, not just oxidize it, and you'll have to re-polish the steel. Depending on your humidity, you might see "fuzz" grow in 15 to 30 minutes.
If you're somewhere where it is very dry (eg, the intermountain west), you might have to knock together a "sweat box." You can do this one the cheap by getting a 4' long cardboard box and putting a can of boiling water into the bottom of the box when you put a barrel in there. Close the box up - it doesn't have to be taped shut, just keep air from circulating. The humidity from the boiling water in the can will fill the box and raise the temp a bit, which will cause the rusty fuzz to form. You should really see results here within 40 minutes.
When you have some rusty fuzz on the gun, put it into the clean boiling water. Wait, oh, 10 minutes. Remove from the water. The reddish rust will have turned black/blue.
Now you take your de-oiled 0000 steel wool and lightly "card" the barrel or steel. You're knocking off the loose rust and leaving only the rust that has adhered hard to the steel.
Then re-apply the blueing chemical, again taking care to prevent drips/runs/sags of the chemical. Let the rusty fuzz form, then boil again, card again... repeat until you get a blue that suits your fancy.
That's how you can learn how to polish and rust blue a gun for less than a couple hundred bucks. Everything you do with rust blueing (the polish, the cleaning/degreasing, the rinsing, oiling after the blue, etc) will be the same if you do hot salt blueing. The hot salts just are another way of forcing black oxide to happen on steel. There's a whole bunch of different ways to force iron or steel to rust black instead of red. And if you get a fine gun or double shotgun into your shop, you know how to rust blue and do the job right, rather than dunk it into the hot salts and ruin it.
ps -- oh, yea... just thought of something: If you want to turn this into a business and you get your FFL, you can start with rust blueing and polishing. For what you should charge for a blue job on a rifle or shotgun, you could pay off all the expenses of rust blueing in probably two jobs:
http://www.brownells.com/userdocs/miscellaneous/shoppricesurvey.pdf