Nitre Bluing Basics 

I realize my comment is pretty long, but you're talking about an art that has nearly died, and will soon be forgotten. I'm passing along a couple of things I know about it, with the hope that you can make use of what I learned, and pass it on to the next guy. I've always known this to be the old method of color case hardening. Not too many folks around today who know anything about it. The bone & antler have already been pyrolized before packing the parts in them. They're really not much more than carbon & a few non volatile compounds that degrade at very high temperature. In an oxygen free environment, such as the metal box everything is packed into, carbon migrates from the pyrolized bone & antler contacting the parts, and gets trapped in the matrix of the steel. It's a lot like a single heat of bloomery steel, when you're turning it into high carbon steel. Due to the relatively low temperature, and relatively solid state of the carbon, the penetration of the casing is only a few thousandths thick. It's durable as all get out though. You can still find pre civil war muzzleloaders with color case hardening done this way, and it still looks nearly as good as the day it was fired. You can also add other stuff to the mix of antler & bone. Turtle shell is a good one. So is a little anthracite. Not too much, because it does still contain volatile compounds. The more materials you put in your mix, the more colors you'll get. The thing I switched to, because it isn't as difficult to source and seems to work better, is used diesel engine oil. The dirtier, more used up, and thicker the better. Keep it in a metal can with a lid. Just heat up your parts, drop 'em in the oil, and temper them back. The outside casing won't temper, and you don't want to grind it down to see what color the bare metal is, so you have to use an oven with a good thermometer. This method gives a black case hardening (graphite color if it's buffed out) that's nearly twice as thick as the antler & bone method, but just as durable.

@@kaisersose5549 Nice write-up, and you're right that good color case hardening is fading from our collective know-how. A real shame because it's functional, and beautiful, when done well. I'm always keen to hear from folks with experience in these mystical arts. Doug Turnbull still does a really nice job of it, and there are a few folks out there like yourself who are keeping it alive and experimenting. I know one gentleman who, and this is going to sound crazy, will pyrolize strips of leather after soaking them in dog urine. He does nice looking work, so who am I to question, but better him than me on that process. However, the process I was originally describing is not a color case hardening in the same vein as what you're describing. The Carbonia bluing method I was talking about uses similar components - various carbon bearing mateirals - but tumbles them around in a furnace like clothes in a dryer, with the part suspended in the middle. The results of the process were a rich, deep, even blue-black color, rather than the swirling, colorful patterns you typically see in color case hardening. It also didn't get hot enough to harden steel, so it was a purely cosmetic process. Unfortunately, being a fairly industrial process, it's essentially out of reach for the little guys, so it basically died out when the big factories switched to more economical processes like rust bluing, parkerizing or hot salt bluing.

That's the old salts from last time he used the pan. The salts dont go bad.

Yes it will that's why he said not to do it

Yes it will definitely mess either temper at least on the surface depending on the thickness of your piece, so you’d end up having to grind off the color anyway, and you’d be betting on not enough heat getting through to mess up the center. Someone else mentioned seeing this process on decorative knives ,but they won’t see barely any use, that may be the only time where I personally would deem it acceptable.

stump remover

You don't watch Midway videos?...

@@shadowblack1987 Not familiar with them . Pray, tell.....

I suspect it was cut up blocks of a previous batch.

No dice bro it only works on regular steel.

He addressed that and said don't do the blade.

I'm gonna experiment with a brand of stump remover I've got with a high purity of KNO3. Nothing valuable until I know how it behaves

Hi James, the Brownells salts have a pink die in them when new. After you use them the first time and they cool down they solidify into a white solid which is what you see in Walter's video (he shows them in his pan at one point). He has just broken up the used salts and added some new to them, probably to replace the little bit that gets dragged out of the pot with your parts every time. You can re-use the salts over and over. Something to remember when using them, if you leave a temp probe or thermometer in the salts as they cool you won't be removing it until you heat the salts up again. Ask me how I know🤣

yevad99 do you know of any other brand than the brownelles salts, I can’t find any others and the only size they seem to sell is that $70 bucket. I just don’t need that much salt

@@yevad99 Thanks for the explanation yevad99. I've never had any experience with this process. 👍

I think in a previous video of his I saw him use the purple 3M tape, apparently it has a plastic like layer, I'm also pretty sure the biggest trick is as applying multiple layers but the best advice would probably be to try and finish everything close to the blade before assembly as any abrasive will wear trough any tape. You know the old prevention is better than cure.

Don't really matter unless you're looking to expose parts of your knife to liquids afterwards in which case there's water/solvent resistant vinyl tapes for that kinda stuff. I for one use plain old painters tape. If I'm gonna clamp the blade thick layers of duct tape on top of that. The trick I suppose is to use tape instead of not using it and using something that comes off easily/doesn't leave a lot of residue so you for one: don't loathe using it and two: don't have to scrub away or use aggressive cleaning agents in order to clean your blade potentially ruining your finish that way.

Yes, but they're easy to scratch

WD40 contains kerosene or something similar, doesn't it? It has both solvents *and* oil.

Not much

I don’t think that’d be a good idea ,going off what he did for the blue color you don’t leave in long enough to get a good temper that would go all the way through your piece, also 600 degrees is going to leave you with a pretty soft temper. It’d be way to soft for any sort of small tool and would probably only suit some kind of axe or chopper. But even then it would be softer than my preference and the problem of the heat not going all the way through would become even more prevalent on those big and thick pieces.

Da Nuke There’s a company that does it, but they don’t go into details as you might imagine. I’ve still very new and this is still a bit above my current skills, but was hoping to get some knowledge saved away for later. Theoretically the higher the temp the less time to temper correct? Is the color change with the salts the same as temper colors? Or do the salts force the color much earlier than a usual heat temper? Could you do a longer (relative to the normal for just the blueing) soak at the lower temperature to temper the blade and still end up in the blue colors? At what temp do the salts liquify? If it’s used on gun barrels I’d assume it has to maintain a good bit of hardness.

Isheian 1: in theory maybe but your surface will still be tempered softer than your center material, and unless you take into consideration the heat conductivity of your specific alloy as well as closely monitoring the time you leave it in and the temperature of the salts you may be able to leave a tempered center in your knife. But this all seems way to elaborate to be worth it to me. 2:the color change from the salts doesn’t appear to be the same, the color change is from the thickness of the oxide layer on the surface of the steel and since in one case the steel is in open air free to react with oxygen while in the other case their submerged in melted salt it probably won’t be smart to base any tempering of the colors the steel gets. 3: according to the video you want a temperature of over 600 degrees for a blue color so I do not think you can get the blue color and have the salt at a temperature low enough to temper your steel. You may be able to temper a chopper with it at a lower temper and still get a straw color but it seems that the amount of time you leave the piece in for effects the color so you could end up with something past blue. 4: I don’t know the melting point 5: I do not know what the hardness of different gun barrels are but depending on what they need the lower hardness could be fine for them or a alloy could be used that has the properties they want. This all said their could be a alloy that would reach a good hardness at the same temperature as the salt I don’t know

Isheian if you want to experiment with it be my guest but if your looking for a way to color a blade I’d look into cold blueing or anodizing (I believe) these don’t damage your temper and they may better suit what your looking for