Thread: Hot salts bluing

Hi guys,

Just thought I would share my experience with my first attempt at hot bluing. This is something i always wanted to try so I did my research and had a crack. Fair to say it was a great success but I learned a few things and wanted to share what happened, as its really not such a dark art that people make it out to be and for small parts in the home shop its quite achievable.

I have an old rifle which I would like to restore and bring back to its former glory. So i thought I will start with another old rifle which is also in pretty worn shape but holds no value to me, as a practice first to learn the skills of bluing and stock refinishing etc. So I started with the trigger guard and a screw.

The bluing process is pretty well documented around various other forums and I went with what seems to be the most common approach, boiling a solution of caustic soda and potassium nitrate and water. There is a bit of a balancing act that goes on with keeping the temperature in the right range whilst constantly adding water as it boils off.

First thing I did was polish up my trigger guard. First mistake too I guess. I went overboard, I polished it until it was like a mirror. And yes it came out astonishingly well but it doesn't look right at all back on the rifle, I should have finished it with 400 or 600 paper for a more 'factory' look. I might even redo it.

Polished trigger guard
20220819_111732[1].jpg

The solution was brought up to temperature and parts put in. I used an old pot from the second hand shop and a cheap gas cooker.
20220819_122040.jpg

After about 40 minutes I took the parts out, washed them with tap water until clean of any residual salts and then oiled them. The screw had literally no preparation whatsoever except de-greasing, most of the old blue was worn off and it had surface rust which I left there. The rust disappeared and it came up fantastic like new.
20220819_125920.jpg

The trigger guard had a kind of blush or fog on it, which was quickly removed with a light buff. It looks every bit as good as I would expect from a professional gunsmith. Except the regrettably over polished finish.

Things I learned:

Boiling caustic soda over 130C is obviously no joke, I was quite well covered with protective clothing, long gloves and face shield but still managed to get a tiny spot of chemical burn about 1-2mm on my arm from a blob of salt flying out of the pot.

The solution as it boils throws salts all over the general vicinity, it just lands everywhere as the bubbles pop and spreads it around like a fine dust. Annoying to clean up.

I had read that doing this in a workshop you care about is a bad idea as it will rust everything around. Sure enough, the table on my drill press and a few other things took a fine dusty looking light surface rust the next day. It was easily wiped off and oiled and no harm done, and no lingering rusting occurred since but I will not be doing this in the workshop again.

Bluing salts 'creep' - that is they work their way up the sides of the pot while you are not using it, go over the edge and onto the bench its sitting on. I have to regularly wipe the inner sides of the pot down as it creeps to avoid that. I need a better storage solution than leaving it in the pot.

Next time I will be better prepared, probably use a better setup, and will be doing it outside.

But the main takeaway message is that this is very achievable and with some care about safety and surroundings it isn't such a hard thing.

Cheers,

ratters

Thanks for that interesting thread

Your trigger guard and screw look great - excellent work - I always wanted to try hot blueing and over the years gathered a folder full of recepies, the big stumbling block for me was a blueing tank and heat source long enough to take a receiver/barrel.

Originally Posted by familyguy

Your trigger guard and screw look great - excellent work - I always wanted to try hot blueing and over the years gathered a folder full of recepies, the big stumbling block for me was a blueing tank and heat source long enough to take a receiver/barrel.

Wouldn't a length of suitable pipe with welded ends and slit down its length sort that problem ?

Originally Posted by familyguy

Your trigger guard and screw look great - excellent work - I always wanted to try hot blueing and over the years gathered a folder full of recepies, the big stumbling block for me was a blueing tank and heat source long enough to take a receiver/barrel.

At some stage I will need this as well. Although I may just weld up a mild steel tank from 2mm sheet. I dont have plans to be doing this a lot so I wont be going out of my way to get really good gear, really I have maybe a couple of rifles that need barrels doing and that's it. I wont tackle a barrel until I have done more small parts and gotten the hang of things a bit more. What recipes do you have if you mind sharing? The caustic soda/nitrate produces a very good black but it wont have any shades of blue to it like some commercial finishes.