doublegunshop.com - home Forums General Discussion DIY Gunsmithing @ doublegunshop.com Heat bluing

On and off, mostly off, I've been playing with heat bluing. I think that I have finally a good way of doing things
and thought I would share it.

I took an inexpensive hot plate and put a half inch thick piece of aluminum on that to distribute the heat and
another block on top of that, to which I attached a thermocouple that came with my $20 digital volt meter.


On top of the block with the thermocouple, I put test pieces, placing a stainless steel travel mug over this
to block air flow.



It took a while to get the temperature stabilized at 295 C, but when I did, I put a skeleton grip cap and screws onto
the block, the screws in the grip cap and the threaded portions dropping into the holes in the block. I ocassionally
lifted the travel mug and observed the changes in the grip cap color. After the last bit of purple had disappeared
and a decent blue was there, I quenched the piece in kerosene. I was very happy with the results. Below is the
grip cap tightened down onto a wooden block. I also made an ebony insert. It looks better in person, than it does in the closeup.



it will go on this project here



I doubt that I am the first person to try this on gun parts, I did find a link to someone using the same method on making
hands for watches via this method. If you are interested in trying this, the link to the color chart below is useful

steel color chart

Fred,
That setup looks much more manageable than simply using a torch. I could Invision A couple different size plates to hold varied projects. Great thinking and innovation.
Thaine

Hi Thaine

Good point about making different sized plates. Compared to using a torch, I think you get a deeper finish by keeping
the piece at a constant temperature for a few minutes. I think that the next time I do this, I will have multiple pieces ready
to go like slide blanks, sling swivel bases, etc. It takes a while to get the temperature stabilized, but once you have it there, you
might as well take advantage of it.

If you cast bullets you can put the piece into the molten lead to do the same thing. You can also temper springs after the quench.

Good show Fred. The way I learned to do this with a torch would be problematic with something like the skeleton grip cap, to keep an even temperature.
Mike

Most folks would accomplish this same thing using Nitre salts. Going above 700-800+° for a few minutes will give you a nice black, uniform finish. I’d rather use a medium like nitre or molten lead to achieve this. I think total, uniform immersion into the medium is a more conducive to finer, more repeatable results.

I would only ever use a touch on items no larger than a safety button, etc. Parts much bigger than that, using a torch is hard to evenly heat the piece to color it and get good results.

Your method is interesting though, no doubt about that.

Le Fusil,
Wouldn't using Niter salts be Niter bluing rather than heat bluing? You are right about using a torch for larger items.
Mike

Nitre bluing is in fact heat coloring. Different temps give different results/colors. The salts do nothing more than maintain uniform heat/temp. A lot of folks temper springs and other steel parts in nitre salts, especially when it comes to “drawing” the steel back after heat treatment, which is especially important when making springs or using hardened mild steel when making a tool.
As was mentioned earlier, molten lead does the same thing.

Quenching in kerosene? That’s ballsy. I would try using something with a bit higher of a flash point (dealing with relatively high temps when coloring with heat, to include hot ignition sources, etc) like a dedicated quenching oil, olive oil, safflower, water, etc.

LeFusil is straight on about the potassium nitrate heat coloring. When you visit gunsmith shops in the UK you will see small 5 inch or so in diameter pans there with the cooled potassium nitrate that the use for heat bluing. I use a torch to do it as I have become adept at doing so, which is an art itself. Proper polishing is a must for successful outcome.

You will have to experiment in how and what you use to hold the screws that you bring into the torch flame (a very small flame) and that the time-ing of leaving the screw in the flame and allowing the heat color gun up to the head of the screw is where the "art" comes in. I normally lay the screw down quickly onto the flat of my vice to cool down. Being able to get the purple violet color of the end of screws that extend through the sidelock plates take a bit of practice. You should note that these small side lock screws (bridle screws and so forth) get to color very quickly and secondly if you want to preserve that special violet/purple color let the screws cool for several hours before you put any light oil on them as oil will darken them.

Sometimes I wrap the screws a couple of turns with small steel wire about 6 inches long to hold them in the flame and with larger screws I hold them with a light pair of hemostats.

If you are using potassium nitrate to temper springs buy one of the Harbor Freight infra-red "point at" temperature gauges. They are very accurate.

Peanut oil has a high flash point and sometimes I use it in spring making.

Wear eye protection--- full face cover when using potassium nitrate.

Bushveld's warnings about using eye and face protection when using molten potassium nitrate are quite valid. As stated, when heated to the melting point, the stuff is around 700 degrees F.

Another precaution I use is to place a long lag bolt near vertically into the molten potassium nitrate before it cools after use. Then, the next time you heat it, unscrew the lag bolt first. This will leave a vent hole going to the bottom of your pot that will prevent a build-up of pressure under the solidified crust when you apply heat to re-melt it. This is not my idea. I read it in Brownell's Gunsmith Kinks, and it is cheap and easy insurance. I have also read that some guys accomplish the same thing by drilling a hole into the solidified salts. But using the lag bolt is very easy, and the bolt head is there to remind you that it needs to be removed before doing anything else.

I mainly use potassium nitrate salts for spring tempering or to blue small parts like screws. I never tried it on larger items such as steel grip caps or trigger guards because I have read that it isn't a very durable bluing process for parts subject to wear. I'm curious to hear if anyone has personal experience to share on durability. I am intrigued by the higher temp charcoal process such as that used by Colt or the Carbonia process used by Smith & Wesson. Obviously, those processes were beautiful and held up well. We had a good discussion about this a few years ago:

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