Hot Blue

[Reg]

Has anyone done this latley, what are you using as a vat to hold the soultion? I think a blacken finish would look great on my M44.
How clean does the metal need to be? I've done a dura coat on a shotgun with great results, would the cleaning procedure be the same?

For a vat or tank, get some 16 ga. hot rolled or even cold finished steel and just bend up what ever tank size you need. Do consider the shape or size of burner you have. Make sure any welds are tight and will not leak. Put bent up 16 ga. handles on each end but NEVER try to pick up a hot tank, only use the handles to move it after things cool down.
The polish will determine the final finish. For cleaning prior to putting the parts in the salts tank, use a pot ( not aluminum if you can help it ) or just make up another tank and use Tide soap in boiling water and scrub everything with a good long bristled scrub brush. There is no need to rinse but if there are areas that might hold this water mixture, be vary careful how you set it in the salts. These small water pockets can cause one heck of a explosion. I use about 1/4 to 1/3 cup Tide to about 5 gallons of water.
I actually use 4 tanks when up and running. One for the hot salts, one for the cleaning tank , one with hot clean boiling water and one for clear cold water. Sometimes and with some metals the salts just don't want to "bite". I carefully take the parts out of the hot salts and quickly put them in the cold water. This creates a "shocking" effect and will sometimes get things cooking. Put some 4 O steel wool in a 3 pound coffee can, cover with water and boil it, pour off the top water and recover and boil again. This removes the packing oil from the wool. If you notice spots or a red or green rust forming on your parts, remove from the salts bath, plunge in the cold water and rub off the rust with the cleaned steel wool and rinse in the hot water tank then back in the salts.
I wear gauntlet rubber gloves, a rubber apron and a full face shield. Hot and itchy but I have seen others get badly burned from this process and thats one club I don't want to join.

[cul8r]

I've done this a few times it's what's called fire bluing by the old timers like colt. I did my 38 super 1911 and it came out perfect. First you need a stainless tank big enough for your project. Then I used straight potassium nitrate which are like tiny pellets the kind I got. You will need a good fire source, propane works fine and the burners you can buy or build easy. You proceed to heat the salts till they melt and become clear liquid. A well ventilated area is a must! You will need a good high temp thermometer 500 f to 700 f range at least. I heated the salt to 560 f before putting the parts into the tank. Your parts obviously have to be prepped perfectly decreased to the max polished or bead blasted with care before attempting this. I wired most of my parts whenever it was possible so tank removal was easy. Now the warning salt peter is a nitrate in other words a oxygenation chemical and at almost 600 degrees f whatever you spill any on like wood floors or news paper instantly sets on fire. Also if you think pouring water into hot oil is a mistake you definitely don't want any water to go into the hot tank, not even a drop. Parts must be agitated when they go into the tank so that surfaces are all wet Simultaneously and the salt reaches all areas as quickly as possible. The parts turn color almost instantly then slowly shading to there final stage which is a brilliant blue. Early in the coloring stage if taken out would produce a lighter peacock blue although very beautiful if desired. After boiling in hot water and oiled with a water dissipating oil they are done. The part I found surprising was it's durability. Outstanding near indestructible. Anyway it's rather simple does a great job and it's rather dangerous, right down my alley.

P.S. as for the fire I used a bar-bq 20 pound propane tank and a giant turbo torch works well for my 1911 but probably not a shot gun due to the length of the tank.

[oldred]

That's NOT fire blue, that's called Nitre blue and it's only useful for certain parts because the heat required will ruin the temper of heat treated parts. Cylinders, bolt actions or other critical parts that are heat treated can be ruined by this method and must not be blued in this manner since their strength could be compromised!

Fire bluing is also for non-heat treated parts and is done by polishing small parts to a high gloss then heating until the surface turns a blue color, it's a beautiful blue but not very durable and suitable only for small pins and screw heads, etc.

[waksupi]

That's NOT fire blue, that's called Nitre blue and it's only useful for certain parts because the heat required will ruin the temper of heat treated parts. Cylinders, bolt actions or other critical parts that are heat treated can be ruined by this method and must not be blued in this manner since their strength could be compromised!

Fire bluing is also for non-heat treated parts and is done by polishing small parts to a high gloss then heating until the surface turns a blue color, it's a beautiful blue but not very durable and suitable only for small pins and screw heads, etc.

The same blue is acquired whether by fire, or nitre. The nitre just makes it easier to control the heat. It can also be done in a lead pot with small parts.

[oldred]

Not exactly, the hot Potassium Nitrate also acts as an oxidizer and imparts a somewhat tougher finish than simple fire, or heat, blue but neither is very durable compared to hot blue or rust blue. Still Fire blue and Nitre blue are two different processes that are done with a different procedure and although Nitre blue can be used on larger parts neither process is really suitable for bluing entire guns because they are not very durable and in some cases due to the temper alteration of heat treated parts can cause safety issues. The OP here has apparently blued an entire 1911 and considering how the 1911 is built he may have (or may not have) created a situation that leads to accelerated wear but probably not caused a safety issue. Something like (for instance) a Ruger SBH in 44 magnum or any gun that is heat treated for strength should not be subjected to either process, nitre blue or fire blue should be used only on small non-critical parts and heating a magnum cylinder or rifle receiver to over 600 degs could be dangerous.

[Hard_Cast]

Waksupi- If doing the nitre bluing in a lead pot, would it not attack and eat at the aluminum walls? I would think this would be done in stainless for best results...

[waksupi]

Waksupi- If doing the nitre bluing in a lead pot, would it not attack and eat at the aluminum walls? I would think this would be done in stainless for best results...

I meant the heat bluing can be done in the lead pot with lead. I would never put niter in one.

I've blued with both methods, and see absolutely no difference in how they wear.

[oldred]

The times I used lead for bluing back when I first started I got better results than simple heat (fire) bluing but then when I switched to using pure Potassium Nitrate I got a deeper better "color" blue. In any case the point of my reply was not so much about the bluing media as the inaccuracies contained in that post, the suggestion that it's a good process for entire guns and the statement that "it's durability. Outstanding near indestructible" when it's a well known fact this process is not very durable if used in high wear areas and is recommended only for smaller parts. However the main point I was trying to make is that this process is not suitable for heat treated alloy steel parts, the heat required is high enough to ruin the temper in these parts. This process is so simple and easy it would be far more common if it were a viable option for bluing entire guns with only a few exceptions, it is not and for a good reason just as the salts are more often used instead of the more easily obtainable and easier to work with lead.


Taken from an article on Nitre bluing,


This is not a chemical means of bluing. Parts to be niter blued are steel which has been polished and cleaned, then immersed in a bath of molten salts; typically potassium nitrate and sodium nitrate (sometimes with 9.4 grams (0.33 oz) of manganese dioxide per lb of total nitrate). The mixture is heated to 310 to 321 °C (590 to 610 °F) and the parts are suspended in this solution with wire. The parts must be observed constantly for color change. The cross section and size of parts will affect the outcome of the finish and time it takes to achieve. [THIS METHOD MUST NOT BE USED ON CRITICALLY HEAT TREATED PARTS SUCH AS RECEIVERS, SLIDES OR SPRINGS. IT IS GENERALLY EMPLOYED ONLY ON SMALLER PARTS SUCH AS PINS, SCREWS, SIGHTS, ETC]. The colors will range through straw, gold, brown, purple, blue, teal, then black. Examples of this finish can be seen commonly on older pocket watches whose hands exhibit what is called "peacock blue", a rich iridescent blue.


Heating any kind of heat treated steel until it turns a deep blue will obviously wreak havoc the temper, springs can even be made by this method by first heating and quenching the newly fabricated spring then placing in the hot solution, either lead or salts, and heated only until it reaches a straw color. If left until it turns as blue as what would be desired for a firearm finish it would be way over-drawn and ruined, the same would be true of other heat treated parts. As for the fellow's 1911 that particular gun being blued by this method very likely would not be a safety problem but he could have caused it to incur serious premature wear problems especially with the slide.

[borg]

I just checked my Dunlap books, could not find any reference to the recipe.
Which one?
Thanks