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:

https://doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=574458&page=1

I totally agree, thank you Lefusil and bushveld.

I've always loved the colors produced by nitre bluing, but have been reluctant to try it because of the associated dangers.
I think that, for the amateur like myself, the method I've tried is a relatively low-cost, low danger way of doing heat bluing.
What I didn't understand. until I started this thread and thought about the replies, was the mentality that I had when I was torch
bluing versus this method. With torch bluing, once I had the color I wanted, I would stop immediately, here once the temperature
is stabilized that you should keep the piece at that temperature for several minutes.

At one time I had access to a whole drum of the salts and thought of setting up a 50 cal ammo can as a tank I could slide under a work bench when not in use. My shop was then and is now in my basement, so I decided to avoid the danger and possible smell, and just go with what I already knew. The smell was why I usually used water hardening steel for screws, D-bit reamers, etc. If I had to quench in oil, I tried to do it while my wife was gone shopping. It didn't always work, and we "discussed" the smell when she returned. I still think PhysDocs hot plate idea is a great one.
Mike

Hi Mike


If you try the hot plate method let me know how it works and contact me if you have any questions. I will do an update
here next time I use it.

Fred

Fred,
Thanks, I will, but realistically I am too old now to finish all my easiest projects. It doesn't help that I can't stand in front of my lathes and mills long enough to be productive. I will have to use the methods I already know. You should learn from my problems and try new ways to do things while you are still young and fit. That way, you can improve things for people coming behind you. A good example is your current project.
Mike

For this type of project, one could consider using an old (small) kitchen pot with clean sand in it. Works just fine to stabilize and even out the temperature, just stick the part in the middle somewhere, near the thermocouple. It's good for uneven parts, but I don't think it's too durable. Thanks for the pictures, and looks like the finish line is in sight.

This golf putter when offered by Scotty Cameron was what they called “oil can” finish. Its probably almost 30 year old. When sold new, they recommend oiling often to prevent rusting. I let my kid use it and after a few years I asked for it back. It had a complete coverage of orange rust. Needless to say I had a few choice words for my kid. So I took it from him cause these have become a bit expensive to Titleist Scotty Cameron putters. I was just going to polish it and hot blue it. But decided to try heat with a torch. It took at least 10 minutes to heat it up to start seeing any color change. But consistent moving the torch around the whole part and eventually it came to the color it is now. I quenched in burnt motor oil. It came out close to exactly like originally new. I’m happy with how the color came out. It has nice pleasing blue and purple finish.

What gauge?

Looks par-fect to me.

When warching the temp he kept his eye on the birdie :-)

Hi Keith

Sorry for the delay in replying, I've been playing around with both methods over the summer and discovered this, that if I take a soft wire wheel used for carding, that the wheel will remove the heat blued finish but not the charcoal blued one. In fact the charcoal blued finish looks better after carding.

Fred

I've been following this thread, so I had to give heat bluing a try. I watched two videos by Larry Potterfield, one titled Flame Blue (), and the other titled Nitre Bluing (). Using equipment on hand (torch, hemostats, motor oil for quenching), I tried it on a couple of cheap machine screws, and here is the result:

I'm satisfied with the results given that this was a first try. I expect I could do better with more practice. My biggest challenge was catching the color change where I wanted it. The screws heated up so fast that when the color change started to happen it was hard to get them into the quench fast enough. Again, with practice and patience I could do a little better.

A couple of things I'd welcome input on - when doing this with heat is the durability of the finish any different than doing it with nitre salts? Similarly, what is the overall durability of the finish? I realize it polishes off easily. Does the finish bring any additional rust protection? Any input is appreciated.

“ A couple of things I'd welcome input on - when doing this with heat is the durability of the finish any different than doing it with nitre salts? Similarly, what is the overall durability of the finish? I realize it polishes off easily. Does the finish bring any additional rust protection? Any input is appreciated.”

The coloring is not durable.

There’s no difference in the colorings durability done with either salts or flame. It’s still coloring done by heat. Salts just heat up and surround the steel in a constant temp bath. Whether you accomplish it by using a flame or salts, all your doing with either method is heating the steel to bring out a particular color whether that be straw/yellow, purple to various shades of blue to black and even gray.

It provides no real rust protection because the coloring doesn’t hold oils like blacking does.

One trade trick when using a flame is to heat the pin or screw from the bottom up. It allows the pin/screw to heat more uniformly. Don’t apply the flame directly to the steel, move the steel in and out of the flame and go slowly.
The higher the polish, the better the color.

The method that works for me for torch bluing small screws is to use a piece of thin, no thicker than .125, brass, drill holes in the brass stock for the screws to pass through, then heat the brass with the torch. The heat goes through the brass to the screws and the color change happens slower so easier to control. When the desired colored is reached just dip into water to stop the change.

For larger screws I have a small can of chips from the lathe and lay the screws on the chips and heat the can from the bottom.

The last screw I heat blued was some 20 years ago. It is the top tang screw on the last m/l roundball rifle I built. I browned the barrel/breech/tang, but I wanted to see how a blued screw would look in the tang. It worked perfectly, gave a fairly bright blue, and has held up fine for all these years. No loss of color.

This is the video referenced in the original post (sorry I started with the last post and didn't realize the video was brought up earlier- thus the edit). It's a very similar method and described by Cold1.

Not gun related, but you might find all of the clickspring videos interesting.