digital thermometer for bluing salt?

Zip · Jun 13, 2021

Need to build a (small) black steel tank for Brownells NitreBlue Bluing. Will only be used for revolver barrel..6" slab barrels, small parts etc.

NitreBlue requires temps up 650F, before I buy a sealed stainless unit was wondering how my digital infrared unit would work. Not sure how accurate they are with liquids.

Another concern is using a "stainless" thermometer in the bluing solution related to contamination etc.

Thanks

trevj · Jun 13, 2021

There are an awful pile of cheap thermocouple temperature displays and Programmable Temperature controllers out there.

As for the liquid temperature with the infrared unit, seems to me the outside of the tank is gonna be the same temp as the salts inside, no? Shooting the side of the tank with the infrared reader is always an option.

CalG · Jun 13, 2021

Zip said:
Need to build a (small) black steel tank for Brownells NitreBlue Bluing. Will only be used for revolver barrel..6" slab barrels, small parts etc.

NitreBlue requires temps up 650F, before I buy a sealed stainless unit was wondering how my digital infrared unit would work. Not sure how accurate they are with liquids.

Another concern is using a "stainless" thermometer in the bluing solution related to contamination etc.

Thanks

Discover from your probe literature just what surfaces the reading is most accurate. (emmissivity!)

Place a piece of that material in the bath or somehow thermally connected and shoot that.

Bob IS your Uncle! And that's not political ;-)

wyop · Jun 13, 2021

1.You can buy small "black iron" tanks for this purpose. Here's one at Brownells:

BROWNELLS QUARTER TANK | Brownells

2. Nitre blueing requires temps up to about only 610F. By the time you get up to 650F, you'll see the blueing wash out. I prefer nitre blueing at a temp of about 590F - that gets me a brilliant iridescent blue on chro-moly steel parts. The lower the temp under 590, the more reds you start to see in the blue. The higher you go over this temp, the more you see "silver" start to wash out the blue.

3. This is the thermometer I use for nitre blueing:

BROWNELLS HEAT-TREAT THERMOMETER | Brownells

Works like a charm. Been using it for years.

NB, I usually blue only pins, screws, small hardware, bits and bobs with nitre blueing as 'accents' on a gun. I don't blue barrels or heat-treated parts in nitre salts.

Zip · Jun 14, 2021

I read somewhere that stainless steel tanks are not recommended for chemical contamination reasons (I have a bunch of those small counter server tanks) but then Brownells instructions mention using a stainless screens and scoop during the process.

Only have a couple of handgun barrels to do, not really concerned with cosmetics and may not do another for a long time.

wyop · Jun 14, 2021

Zip said:
I read somewhere that stainless steel tanks are not recommended for chemical contamination reasons (I have a bunch of those small counter server tanks) but then Brownells instructions mention using a stainless screens and scoop during the process.

Stainless hasn't been an issue when I've been nitre blueing. There are stainless dippers for nitre salts and screen containers for small parts that are made of stainless. Plenty of fellow gunsmiths have used stainless pots on a stove for the job.

You can even blue stainless with nitre salts. You might have to run the temps up/down through the range to see where it starts blueing.

Zip · Jun 14, 2021

wyop said:
Stainless hasn't been an issue when I've been nitre blueing. There are stainless dippers for nitre salts and screen containers for small parts that are made of stainless. Plenty of fellow gunsmiths have used stainless pots on a stove for the job.

You can even blue stainless with nitre salts. You might have to run the temps up/down through the range to see where it starts blueing.

Thanks...Just about have a steel tank fabricated...need to fire up the TIG tomorrow and just ordered a new thermometer. May experiment with some stainless in the future.

wyop · Jun 14, 2021

Excellent! Best of luck. If you have other questions, please ask. I've done a bit of nitre blueing and might be able to help.

Oh, one more tip, and please don't get the impression that I think you're a klutz or something. This is me taking off my gunsmith's hat and putting on my volunteer firefighter's hat about safety.

Brownells Nitre blueing salts are a mixture of Potassium Nitrate, Sodium Nitrate and Sodium Nitrite (please see SDS link below). When heated to the blueing temp (> 570 degrees F), you have not only a molten salt that has more than enough heat to light paper, wood, plastics, etc on fire - you also have a very, very strong oxidizer right at the point of ignition as well. It's like starting a fire with liquid oxygen already covering the flammable material.

While I was at Trinidad, I saw a guy tip over a lead pot filled with molten nitre salts on a wood workbench top.

The wood top burst into flame instantly - with a very, very vigorous flame.

Please try to use these salts where, if they spill, they can't ignite flammable materials.

https://www.brownells.com/userdocs/MSDS/082-090-019_NITREBLUE (TM) BLUING SALTS 10 LBS.pdf

partsproduction · Jun 15, 2021

If I may interject a question, won't 590F degrees be more than high enough to effect the hardness and strength of heat treated parts?

Zip · Jun 15, 2021

partsproduction said:
If I may interject a question, won't 590F degrees be more than high enough to effect the hardness and strength of heat treated parts?

I was wondering that myself because some articles mentioned using NitreBlue in the hardening process. I'm building another S&W K frame with this Douglas chrome molly barrel. The other blue Model 10 K frame I built has a Douglas stainless barrel and shoots "extremely tight groups" at 50 yards (my competition goal). This "in the white" barrel is to be installed on a stainless Model 64 so I need to blue it before installing it. My concerns are property changes with the (NitreBlue'd) chrome molly barrel, once torqued into position - it will need to be gapped and the forcing cone cut with Brownells reamers.

BTW: I only want a protective finish on the barrel...not concerned with looks.

Pete Deal · Jun 15, 2021

I do my own hot black oxide. Temp is about 290 deg f. I think blueing is about the same not 500-600.

Regarding the temp probe….
Like blueing salts stainless is not recommended. So i got some steel tubing from mcmaster. About 1/4” od. Stripped some fiberglass type k thermocouple wire and slid it down the tube till it stuck out the other end. Then tig welded the end shut. The wire gets fused into the weld. The tube end closure makes the thermocouple junction. On the other end where the wire comes out of the tube I put some heat shrink with adhesive inside to form a strain relief. There are quite a few nice deals on ebay on nice hand held omega thermocouple meters. You’ll need a type k plug as well.

wyop · Jun 16, 2021

partsproduction said:
If I may interject a question, won't 590F degrees be more than high enough to effect the hardness and strength of heat treated parts?

If you're seeking to keep steel at full hardness after quenching, yes, it is hot enough to draw out some of the hardness.

This is why nitre blueing is used typically only for pins, screws and small parts.

wyop · Jun 16, 2021

I do my own hot black oxide. Temp is about 290 deg f. I think blueing is about the same not 500-600.

Black oxide blueing and nitre blueing are working in two different ways.

Black oxide is creating a layer of Fe3O4 on the surface of the steel. The blueing salts for black oxide blueing will be mostly sodium hydroxide (lye) and maybe some sodium nitrate. The salts are oxidizing the steel directly.

In nitre blueing, what you're seeing is a heat staining of the steel. I could give you the exact same results as nitre blueing without any salts whatsoever. You can try this for yourself if you have a heat treatment oven. Simply clean a piece of polished steel with some acetone or brake cleaner to remove all oils, then carefully place it on some stand in the heat treatment oven to allow the hot air to get all around the steel. Set the oven for 575 to 590 degrees F, and walk away for a couple of hours. Turn off the oven, allow the steel to cool down. It will have the same sort of blue as you get with nitre blueing.

trevj · Jun 17, 2021

Pete Deal said:
I do my own hot black oxide. Temp is about 290 deg f. I think blueing is about the same not 500-600.

Regarding the temp probe….
Like blueing salts stainless is not recommended. So i got some steel tubing from mcmaster. About 1/4” od. Stripped some fiberglass type k thermocouple wire and slid it down the tube till it stuck out the other end. Then tig welded the end shut. The wire gets fused into the weld. The tube end closure makes the thermocouple junction. On the other end where the wire comes out of the tube I put some heat shrink with adhesive inside to form a strain relief. There are quite a few nice deals on ebay on nice hand held omega thermocouple meters. You’ll need a type k plug as well.

Yeah, have heard of guys tacking the individual leads on opposite sides of the block they were heating, and getting accurate results. I have made a couple probes up as you describe, and they worked very well. If a guy really wanted to splurge, there are sources for the ceramic bead insulators, so you can be certain that the wires do not ever touch the inside of the pipe used.

Which makes the guy that was trying to sell our shop a multi-thousands of dollars spot welder to make 'accurate' thermocouples, even funnier.

Pete Deal · Jun 17, 2021

I agree the little ceramic insulated wire would be a better choice. Mine is made with stuff I could get cheap and that's not quite as common.

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