Are you at least 18 yrs old? Reason that I ask- (a) I can't look thru the computer and see you, and (b) the components of most hot bluing salts are caustic as hell- will eat the skin right off you if you are not careful with them. So they do not sell to minors.
Outside of that, there is no license/ password/ secret handshake. If you want to try your hand, couple of things to remember-
Metal prep and polish are a gotta do. Bluing does not cover pits or scratched metal. 90% of the work is polishing. Doing so without rounding over sharp edges or dishing out screw holes is the hard part.
Do not hot blue things with soldered parts- like double barrel shotguns. Bluing salts will attack the solder. Do not blue things that are not steel, the salts will dissolve aluminum. Do not blue late model Winchester lever actions- wrong alloy- either will not blue, or will turn purple.
Degrease- and then do not touch with bare skin- before bluing.
You need a bluing tank, and a boiling water tank, and source of heat. Do not let any water hit the bluing tank once heated- you will get an explosive spatter of caustics.
Wear GOOD eye and face protection.
I have done a few blue jobs- mainly to see if I could- and they turned out well. But with the cost of chemicals and equipment, for a one time, you will likely be much better off finding a good smith that does good bluing, and pay him.
IF you decide to go forward with this, why not do a writeup for the others here, and include a few pictures?
Yeah I am 19 years old. I want to blue most of the parts on my Gatling gun that I built. My first problem is I have several different kinds of steel on it. Some hot rolled and some cold rolled steels. My side rails are A2 steel and they are 20 inches long. I am going to need a big tank to blue them. My barrels are 416 stainless so I got them chrome plated because it cannot be blued. How much of an investment am I looking at for the whole setup?
IF you have parts that are polished, disassembled, degreased, and ready for the tank, a smith would charge you quite a bit less than if he has to do all the prep (labor intensive). Your cost to DIY will depend on the size of parts to be blued. However, doing it right is likely to cost you quite a bit more than a smith would charge you. Too many variables to give you a simple answer- other than do not try this on the kitchen range. Hot blue is a supersaturated solution of salts and water, and boils above the boiling point of water.