Heat blueing parts of knives

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terrinecold

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Oct 3, 2016
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I am thinking that I would like to use the technic used in this video:
to blue some parts of my knife (obviously not the blade but I am thinking about the spring lockbar and bolsters). I wonder if anybody has advices on:
  1. Would it be a good idea
  2. How to do it (I plan to do it similarly to what the video is showing but I don't have the kind of shop this guy has. I don't have brass shavings lying around for instance or a good way to build a brass box)
When looking for blueing on the internet I mostly see things about gun blueing which is pretty different from this technic which is typically seen on watch parts and (to my eyes) looks really really nice.
 
Heat bluing works fine.

However, for a better blue on knife hardware, set up a niter bluing po
It is nitrate salts that melt around 450F. Put the parts in for a few seconds to a minute and they come out beautiful blue. Hightemptools sells the salts an well as places like Brownell's. With a tight cover on the pot when not in use, you can re-use them for years. Check the info with the salts you buy, but most work in the 500-550F range.

This is a good project for a home-made low temp salt pot. A stainless steel pot, hot plate, PID, and stainless clad TC will work fine for a simple unit. Control the hot plate with the PID.
A small pottery kiln that is converted to PID control and a welded up stainless tube will make a suitable low temp salt pot that will blue up damascus blades. On blades, you only put it in the 500F salts for a few seconds.

The same setup can be used with a second tube that has low HT salts for marquenching. This is the best way to quench blades and avoid warp and twist. Straightening is simple since the blade never cools past 380-400F. Once straight, just hang in air to cool off the rest of the way. I don't think there is a better quench for a non-hamon sword blade than a low temp salt pot. My next big purchase is one of the new commercial units.
 
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Heat bluing is commonly done to screws and other small gun parts. While attractive, NO bluing technique wears well. This is why it is generally only done to low-wear surfaces like screws.

You don't need brass boxes, etc. to accomplish it. All you need is even heating of your clean steel. This can be accomplished easily with a torch after some practice.
 
Thanks Bill and thanks Stacy.
I'll try the torch before the salt as the set up you suggest sounds a little complicated. It does sound like a nice project but probably not for now.
Regarding the wear, would you consider that the bolster, lock bar and back spring are low wear? I guess that the lock bar is probably the one which will be most subject to wear of the three.
 
It doesn't have to be a complicated setup. You can heat the salts in a pan on the stovetop and check the temp with a cheap HF a laser thermometer.
My suggestions were for a permanent bluing station.
 
I'll buy salts and try that. I tried with just the torch over the WE and couldn't get good results. What do you think about using a solder port there are some very cheap ones on amazon. In combination with a laser thermometer that seems like something which could be made to work simply (without cooking weird thing on the stove, I can already hear what my wife would have to say about that, after tempering in the stove I quickly bought an old toaste oven for the same reason)
 
Probably not what you want to hear, but I tried various forms if heat bluing for a couple weeks, couldn't get a result remotely close to what I wanted. Set up proper caustic hot bluing and never looked back.
 
A cheap solder pot is lower temp than needed. The ones that go to 700F are pricey. A lead pot is higher than needed. Use a cheap hot plate. The salts only need to be heated to around 500-600F. An old stainless steel sauce pan will work for the pot.

When done for the day, let the pot of salts cool to room temp and place some plastic wrap over the pot, and a rubber band around the rim, to keep out atmospheric moisture.

I just took a look to see who is carrying it right now. Brownell's seems to only have it in 10 pound tubs. HHT&R only has low temp quenching salts. They will work, but don't produce the wonderful blue color that the Niter-Blue salts do. Mayby you can split a tub with a few knifemaking buddies.
https://www.brownells.com/gunsmith-...ng-salts/nitreblue-bluing-salts-prod1105.aspx
These salts are used between 570F and 650F.

IIRC, one of the knife supply catalog companies used to sell it in one pound bags, but nothing comes up in a fast search.
 
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thanks for searching for me. I could deal with a hot plate and old sauce pan. 10 pounds does seem like a lot, I'll search more to see if I find smaller quantities. I am the only person I know who makes knifes so sharing will be hard.
 
I just ordered 2lbs of potassium nitrate and 1lb of sodium nitrate for $20 shipped. I'll let you know how that works for me.
 
Haven't found sodium nitrate yet, potassium nitrate is sold as stump remover up here. That and lye makes a great hot (caustic) bluing mix. Jet black.
Mind you we don't nearly the regulation on things that can be made to go boom up here.
 
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I'm not too worried. I didn't get any visits when I bought 20 lbs of ammonium nitrate for targets and hot bluing :D

Look for bio diesel suppliers. They sell all kinds of ates and ites.
 
This is my experience:
I use a mixture of 2/3 of sodium nitrate and 1/3 of potassium nitrate. Potassium and sodium nitrates are very used in agriculture so you can find them at farm dealers (here in Italy they sell them to 50 pound bags, the hard thing for me is to be able to buy only 2 pounds). As a container you need use inox containers, I used those that contain ice cream, including lid should cost around $ 12. When the salts dissolve they are around 640°F (340°C), I recommend the melted salts do not like water .... CAUTION!!!!!. Normally it takes a few minutes 2-4 to paint the steel but it is good that every now and then take the knife out of the solution and observe the color it has reached (usually before the gold color, then the blue ..... to the bronze) if the color you do not like immerses again and continues. When you reach the desired color, you have to block the reaction by cooling the steel: I dip the piece into boiling water (you will get some sketch of water in contact with the steel.... Attention!!!), after that I dip the piece into water at room temperature.

I know another recipe (that I did not use), in 5 liters (1.3 gal) of water you put:
- caustic soda 2500g (5.5 pound)
- nitrate sodium 500g (1.1 pound)
- sodium nitrite 120g (0.26 pound)
- Trisodium phosphate 60g (0.13 pound)

when the salts dissolve and the water is boiling, soak the piece to be colored, the temperature should be between 120 and 140 ° C
 
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