When I read a knife has been "Hot blued" I like the way this looks

A.W.Stovall

A.W.Stovall

Well-Known Member
I know it uses gun bluing stuff , but for us knifemakers what is involved what do you use and why and how?
Thanks Anthony
 
There are several formulas for bluing. Regular bluing salts are a mixture of sodium hydroxide (very caustic). This is heated to 295 f and the very clean steel part is submerged in it for some time. This forms a dark blue oxide layer on the steel. Another method is nitre bluing. It can be a lovely purple blue, but, it requires temps in the 575f and higher and will damage the temper on a knife to the point that it would not make a very good user. You can buy the salts from Brownells and then you need a good heat source like a double propane burner, a thermometer, good ventilation and a mild steel container large enough to hold what you want to blue. You must get the piece extremely clean or it will be splotchy. I used 8# of sodium hydroxide (available as a drain cleaner) in 1 gallon of distilled water to achieve a great blue on several pieces. Storage of the material sucks. It semi hardens and seems to creeps out of a covered container. You must nutralize the piece after its done and washed off. Vinegar will work, then it needs to be coated in a good light oil.
 
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Never tried the nitre bluing, but, I think you can get supplies and instructions from Brownells. I think that it is about the same as caustic bluing, just another chemical and a way higher heat. For something like guards you wouldn't need a very big pot. I used a enameled roasting pan for the knives I did in the caustic.
 
I personally think that Nitre Blue is the ticket for bluing hardware. You can produce anything from a "Luger Brown" all the way through the bright blues. The whole key to how the end produce appears is the finish you apply BEFORE bluing. If you bead blast it, then blue, the color will come out looking pastel. Satin finishes will produce satin looks, and in order to get the "pop your eyes out" blue, the piece must be mirror finished.

None of the bluing processes produce a finish that I would call durable. However, compared to other methods, Nitre blue has proven itself to be the most durable that I have used. Also, be aware that Nitre blue is not so much a chemical process, as it is a heat sink process. I've spoken with the techs many times at Brownells.....they are great folks, and if you have questions, I would recommend calling them for the answer(s).
 
What, Or should I say How is Nitre bluing achieved?:les:

I've watched Jim Siska blue fitting in his Tempering oven just with certain temperature of heat for a certain amount of time.He can achieve many different shades of blue this way. The Last fittings he did for me came out a beautiful Aqua blue. As Ed said, The parts were perfectly mirror polished to start. I know this type of bluing does not last well though.
 
Rust blueing

I rust blued this one. Made it rust then boiled it in water to turn it black. It's a lot more durable than cold blueing.
 
Another thumbs up for cold rust bluing. I just did a full coat of chain maille and sword. Turned out beautiful and produces a very tough finish.
 
Yes, 0000 steel wool. I've only done this once, the next time I think I will use 1200 grit sand paper on the flats and steel wool everywhere else, I think that will speed things up.
 
Calvin Robinson said:
I rust blued this one. Made it rust then boiled it in water to turn it black. It's a lot more durable than cold blueing.
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That's a nice looking dagger Calvin what did you use for the scales looks like micarta with micartsa pins and screw? nice job on the sheath also looks very well formed.
 
whiteeugene said:
That's a nice looking dagger Calvin what did you use for the scales looks like micarta with micartsa pins and screw? nice job on the sheath also looks very well formed.
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The gaurd and pommel are made from black linen micarta, they are screwd on, the handel is neoprean, it is glued and pinned with black linen pins. Thank's for the compliments.
 
000_1010 (Small).jpg000_0471.jpgFrom my very limited experience carbon steel changes color at specific temperature. yellow 400f, straw 500f, purple 550f, dark blue 600f, red/grey 1000f . I'm sure this differs along with the carbon content. I have colored many knives (granted safe queens) but some colors fall into the tempering range and don't hurt anything.IMHO On some damascus you can get multi colors because of thickness diffs and shealding thro silver in the mix.
 
shakie said:
Try www.SMEX.net and scroll to color chart
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Is that the right link?

smex.net smex.net


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Das Leere lernen, Leeres lehren?- The void learn Empty teach? -

Spach ich vernünftig, wie ichs angeschaut, I Spach reasonable, viewed as self,

Erklang der Widerspruch gedoppelt laut; Heard the loud opposition doubled;

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Zur Einsamkeit, zur Wildernis entweichen, For solitude, escape to the wilderness,

Und um nicht ganz versäumt allein zu leben, And not entirely failed to live alone,

Mich doch zuletzt Me at last dem Teufel übergeben. the devil passed.
 
I have blued about every way under the sun. I prefer hot blueing, I use Oxynate 7 salts from Brownells. You get a beautifull black/almost dark blue finish. The finish reflects the finish you put on the steel. IE if you blast parts you get a matte black, if polish the parts you get a polished black/blue. The salts are caustic, Meaning you do not heat inside, if you get some on your shoe leather it will eat the leather in just a few seconds, the fumes make you itchy as hell and if you get some in your eye you will go blind in short order. I mostly use this finish for pistols I build but will occasionally use it to finish knife parts or tools. For a beginner I would recommend parkerizing instead, far less dangerous and you can do it inside if your careful.
As for Nitre blueing I find it not as durable as hot blueing, but the different colors you get are a cool bonus.
Hope this helps.
Chris W.
 
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