I keep hearing all theese terms like "hot" or "cold" or "heat bluing". but i dont know a definite answer as to wich is safer for the metal. can anybody tell me what method is more reccomended than others?

Hot bluing consists of soaking the piece to be treated in hot blueing salts for a specified period of time, This method can yield outstanding results but requires specialized equipment and some level of skill. Cold blueing on the other hand is a compound that is rubbed on the part to be treated and is added to till the desired coloration is achieved. Cold blueing is a fairly simple and inexpensive method. I have personally achieved some very good results with coldbueing. I am familiar with the process of hot bleing but have never personally done it, so I am sure that others can add more personalized recommendations.

Both methods rely on very careful preparation of the material to be blued. Imperfections in the finish will show in either way and the part must have no contaminants (oil, dirt, rust, etc.) on it to have a successful treatment.

Neither has much effect on the metal as they are surface finishes.

Now depending on the alloy; the temperature of hot blueing may be above the tempering temperature if it has been hardened and this may be a consideration; but for mild steel it has no effect.

Note too that there is also temper blueing; just heating the steel up to the temp that has the colour desired.

Also: Rust blueing - allowing / encouraging the part to rust in a controlled manner, then boiling it in distilled or rain water to change the rust to black. This is a very old gun finish technique.

I'm pretty sure that alloys with a high nickel content will not take blueing (either hor or cold bluing). I had a part for a guitar (used to be chromed) hot blued, and a very small crevass where I couldn't grind off the base nickel plate never took the bluing, and the nickel contrasted brightly.

I guess that's one of the reasons why nickel alloys are popular choices in pattern welding when the blades will be blued for corrosion resistance.

but dosn't heating the metal past the normal point of workability make it brittle when it cools?

It never gets that hot. You are talking about a chemical process that functions around 280 F. You can blue heat-treated parts with no ill effects. As mentioned, cold bluing can be done at room temperature with decent results.

If you are referring to torch bluing, the heat can be around 600-700 degrees so again, that will not affect mild steel (although it might cause issues with heat-treated parts).

First of all to become brittle you must be using a steel with a high enough carbon content to harden when quenched. Most items are made from what is called mild steel and will not harden.

Next to harden you must heat to above the curie temperature, 1414 degF, when the steel is actually glowing. Hot nitre blueing or temper bluing are way under this temp.

Next you must cool off the steel fast enough to create martensite instead of pearlite which generally involves a quench of some type. Most hight Carbon steel alloys heating and letting them cool in still air is called normalization and will soften them if they have been work hardened.

I'm pretty sure that alloys with a high nickel content will not take blueing (either hor or cold bluing). I had a part for a guitar (used to be chromed) hot blued, and a very small crevass where I couldn't grind off the base nickel plate never took the bluing, and the nickel contrasted brightly.

I guess that's one of the reasons why nickel alloys are popular choices in pattern welding when the blades will be blued for corrosion resistance.

High chromium too I think(like stainless steel). Also applies to Parkerising. (This explains the characteristic look of the M1 rifle's muzzle; the Parkerising rubbed off the stainless gas tube almost immediately but not the plain carbon steel barrel.)

I recently found a method of blueing where you dip the item in ferric chloride for a few seconds rinse and put in an oven for 30 minutes. does anyone have experience with this?

I have a full hot caustic bluing setup for bluing rifles.    And I sometimes do the  rust bluing thing.

Tanks below.  Hot, sweaty, nasty work.   The bluing gear is under a lean-to roof behind the shop, with three sides open for ventilation.   Bluing salts eats everything, so the stuff cannot be in an enclosed shop.  Note the floor:    A bed of gravel, then pallets, then rubber horse stall mats to stand on while tending the tanks.    The salts will even eat concrete.   The roof is fiberglass greenhouse panels over treated wood joists. 

The dark vile looking stuff in the rusty tank is the bluing salts.   I run the salts at 285 degrees F, so no harm to heat treated steels.  The stainless tank in front with the  frothy white liquid contains the cleaning solution at 200 degrees F.    The caustic tank has to be mild steel, stainless steel tanks for the salts will give a ugly bluing color.

Other tanks are cold water rinse, hot water rinse at 200 degrees, neutralizing bath at 140  degrees, and water displacing oil bath.   I leave the gun parts in the water displacing oil over night.

 

From the time I light off the first burner, until I dump the parts into the water displacing oil, takes about 4 hours.      Not counting the metal prep!!

 

Looks like this when complete.   460 Weatherby on the left, 458 Lott on the right.

 

 

 

 

I once had my chainmaille shirt hot blued, (about 40 years ago).

DuLite is not supposed to creep like the Brownell's salts we used. 

To get bluing to retain better  do not give it  a high polish, we stopped at 230 grit, and I always finished by hand as the buffer seemed to close the pores in the barrels up as it smeared the surface.  Sanding by hand seemed to leave them open, and we got a lot better results doing so.

Warming the piece up some will get cold blues to bite better and gives better results.

After trying salt, I realized I had something here.  It takes 24 hours and I did no experimenting after that so other steel types should be tried. The blueing is a lighter look but after waxing it will darken. Might protect my bare steel parts over winter in the shop.  If you have to sand or grind something, this will blue it.   I dont want to do hot bluing as the hardness is set  into this hole fuller.  Note that I didnt stick it all the way under the liquid so you see untreated steel  next to treated steel.   A poor mans bluing?

SLS