Hi all! I would like to set up a small hot blue tank for screws, top levers, safe buttons, trigger plates and 4end irons . What are you happy with and what is the procedure? Do you need a separate room and multiple tanks?

Tracy,
I thought at one time about doing this using 50 caliber ammo cans on a camp stove. I even went so far as making baskets for the parts. Like a lot of us, I got wrapped up in something else and didn't get back to it. Maybe you could pick up the ball, I would be interested in how it works out. At the time I had very little space and thought it would be convenient to blue outside under the patio cover then put the tops back on the cooled can(S)and store them out of the way. Good luck.
Mike

A friend used to do this.
He had 2 propane fired tanks, one hot water, one solution.
Bluing ran about 320F, so lots of steam and humidity.
Also fairly dangerous if not careful.
Heat de-greased parts in hot water
Shake off ALL water
In hot tank till blue
Rinse in hot water
Dry, and oil
Sorta like that.....

Read Brownells instruction and be careful with the stuff. best use a stainless steel container a lot bigger than you think you need ( it splatters at 380 degrees) and best do it outside or in a well ventilated area. People that I knew that hot blued die early, I don't know if it a result of this or not just saying.

Ok, enough from the experts:

I’ve been offering hot (caustic) bluing to my customers for 25+ years. I’ve also used most of the major brands out there: Du-Lite, Brownells, Williams and once or twice my own brew; so I might know a little something about it.

Depends on what you want to do: if it’s for an occasional bluing, screws, top levers, safe buttons, trigger plates and 4end irons etc.… farm it out or Nitre Blue the parts.

First of all, it’s super-heated concentrated lye (295 deg), so it’s really not fun stuff to play with, lye burns hurt… so…protective equipment.... Don't know where folks are getting 320/380 from.

Ventilation is a must.

Have a dedicated place to do it, lye destroys a lot of things… brass, wood, aluminum, basically anything organic.

When not in use… the salts creep, they will creep up and over the tank, and down the sides and onto anything below it, with the potential to mess it up… Wood floors… bad idea.

They are not cheap, just got another 5 gal bucket of salts in recently $325, the hazmat shipping adds a lot.

It does blue parts quickly, once up to temperature… but it takes a while to get it up to temp 45 minutes.

The salts have a fairly narrow operating range, you either add water or add salts to keep it in that range; adding water to a solution that Is super-heated (295) can be an emotional event, think what happens when you put water on a hot skillet… immediately turns to steam… same thing, but with lots of splatter (think super-heated caustic lye).

I do lots of finishing work in the shop: Color Case Hardening, Nitre, Charcoal Bluing , Rust bluing Caustic Bluing, Caustic Bluing is my least favorite.

Hard to argue with what Mike says. Miserable job. I have a 1/2 tank for small parts but to be honest I will almost always use another method to get parts black if I have a choice. I set the tank up specifically to black a Winchester 21 and it is perfect for that. Otherwise I will express blue, Nitre blue or slow rust blue most items. I use black iron tanks for my caustic blue.

I have been using Unibath in a stainless steel salad bar tub about of 1/3rd of a tank for forend irons, trigger guards and other smalls. It likes to work best at about a 275F slow rolling boil. I like it because it has a nice deep black, only need one heated tank and is not picky about cleanliness . Polish the part wipe off with a rag dampened with Denatured alcohol drop in tank till happy with color and dunk in cool clear water then oil. Unfortunately Unibath is no more and I will eventually need a replacement. It's the only hot salt solution I have experience with.Is something comparable out there?

I don't do hot stuff any more, rust blue everything now. In the past I used the below. It's from Roy Dunlpap's book "Gunsmithing".

Lye 2 parts (or sodium hydroxide) Lye is usually 94% NaOH
Ammonium nitrate 1 part (ammonium nitrate fertilizer 33%)
Water see below

Solution: 5lbs lye
2 1/2 lbs ammonium nitrate,
per gallon of water

Work temp 285-295 F. Rinse in warm/hot water.

Gives a nice dark blue/black black/blue depending on the steel.

Tracy, most of the parts you want to blue don't sound to me like ones that would have been hot blued to start with. You may want to consider Laurel Mtn Express Blue. It's a rust blue that's super easy for small parts. It takes no special equipment, and it happens fast.

Which parts would have been hot blued on guns made prior to 1940 or so? I had the impression that the barrels were rust blued, the furniture was hot blued, and the frame was case colored. Is that incorrect?

I'm thinking primarily of British made guns, and it occurs to me that the answers could be geographically specific.

Follow up question: Is there any role for tempering screws to the color one wants? (I'm assuming that would not be a good idea for the actual furniture.)

It would depend upon the maker and time frame but hot caustic blue was not something that was standard in the British trade at that point in time. I think you will find that Charcoal blue was the standard for furniture with nitre blue often being used on small parts and screws.

Well I don't know much about British guns, but I can talk a bit on American guns, specifically Winchesters.

Winchester didn't start hot bluing their guns until 1939, salts were supplied by Du-Lite.

Prior to 1939, frames and other "smallish" parts were Machine AKA Carbonia Blued, That started around 1903. Process supplied by the American Gas Furnace Co. barrels & mag tubes were rust blued.

Prior to machine bluing, Winchester Charcoal Blued frames and larger components: bolts, buttplates etc, Smaller components were nitre blued.