Hot Bluing at home

[guzzitaco]

Hot Caustic Bluing

As promised, here is a detailed explanation with formula and procedure on how to hot blue at home.

Introduction: I started to search an alternative finish method because I wasn't happy with cold bluing or rust bluing. The results, color and longevity of those finishes wasn't what I was looking for.

I am a hobbyist not a gunsmith or a chemist. I like learning on projects and building things with my kids so they understand the sense of accomplishment when achieving a goal. I don't think this should be intended as a cost saving initiative. In my opinion, if you want to save money perhaps you should cut other expenses in your personal life.

All this info I found online and I cannot take credit for it. I will just try to edit it and add my own learnings.

Disclaimer: HOT CAUSTIC BLUING IS DANGEROUS STUFF. THE BATH BOILS AT 280 TO 295 DEGREES AND THE CAUSTIC SOLUTION CAN BURN YOUR FACE, SKIN, EYES. VAPORS SHOULDN'T BE INHALED.

I CAN NOT STRESS ENOUGH HOW IMPORTANT IS THE PERSONAL PROTECTION EQUIPMENT WHEN DOING THIS: CHEMICAL GLOVES, RESPIRATOR, FACE MASK, LONG SLEVES, CLOSED SHOES, LONG PANTS AND APPRON IS THE MINIMAL PROTECTION GEAR THAT YOU SHOULD WEAR. THIS THREAD IS FOR INFORMATIONAL POURPOSES ONLY. IF YOU DECIDE TO DO THIS, YOU DO IT AT YOUR OWN RISK.

Personal Protection Equipment you should wear


First aid information worth reading just in case: Chemical burns: First aid - Mayo Clinic


Setting your expectations: It is very likely that initial results will not be outstanding. If you are looking for fast and outstanding result, perhaps you should consider sending your slide to a qualified gunsmith.

The good, the bad and the ugly

The good: you might end with a slide like this


The bad: you must deal with this


The ugly: if you are not careful and don't wear personal protection equipment this could happen to you (or worse, you could burn your face, your eyes, etc...)


So, if you are still interested in learning about hot bluing follow this thread...

more to come

 

[skjos]

Wow, are those chemical burns or burns related to the temperature of the solution?

 

[guzzitaco]

Wow, are those chemical burns or burns related to the temperature of the solution?

that is a sodium hydroxide burn...not mine...related to the temp of the solution and nature of caustic reaction...

"Exposure to sodium hydroxide solid or solution can cause skin and eye irritation. Direct contact with the solid or with concentrated solutions causes thermal and chemical burns leading to deep-tissue injuries. Very strong solutions of sodium hydroxide can hydrolyze proteins in the eyes, leading to severe burns and eye damage or, in extreme cases, blindness."
cdc.gov

The solution generates a reaction that takes it to 240 deg without heat being applied...when heat is applied, it gets to 295 and higher...(if not controlled)

Must wear PPE and be careful...

For more info please read:
Please read: ATSDR - Medical Management Guidelines (MMGs): Sodium Hydroxide

 

[BC38]

Yeah, caustics are far more dangerous than acids. The human body is naturally slightly acidic.

Caustics are the opposite end of the PH scale from acids, and acids and caustics create some pretty energetic reactions when mixed. Way more so than mixing two acids together or mixing two caustic compounds together.

A caustic compound on your slightly acidic skin makes for one of those high energy reactions - which means it does MUCH more damage.

For example: battery acid is pretty strong, but a drop on your skin won't even burn you if you rinse it off within a few minutes. But a drop of lye that is the same strength as the battery acid will burn you instantly and eat through your skin within a few minutes.

 

[Neversink n Klapperthal]

what could go wrong?

 

[guzzitaco]

be prepared

what could go wrong?

Accidents happen...that is why is so important to wear personal protection equipment when working with a caustic reaction...

Also, go through the mental exercise: what would I do if something goes wrong?

I don't like doing any of this alone. I always have a friend or one of my kids to help. Someone that can dial the phone in case of an emergency, or grab a water hose for an emergency wash...

 

[guzzitaco]

Definitions

Some definitions

Bluing:
Bluing is a method commonly used on gun metal in which various gun parts are submerged in caustic hot salt baths (caustic reaction) for a period in-order to attain the coat. This isn't the only method to obtain the oxide layer, it's but one of many. Some sources have stated that bluing provides rust resistance while others are skeptical since most oxide layers because of the process are merely 2.5 micrometers (0.0001 inches) in thickness.

Caustic reaction:
Caustic corrosion/gouging occurs when alkalinity of boiler water increases. Caustic corrosion is also called caustic attack. Caustic corrosion develops from deposition of feed water corrosion products in which Sodium Hydroxide (NaOH) and other components can concentrate to high PH levels. At high PH level corrosion occurs forming oxide.

Sodium hydroxide
Sodium hydroxide is also known as lye or soda, or caustic soda. At room temperature, sodium hydroxide is a white crystalline odorless solid that absorbs moisture from the air. It is a synthetically manufactured substance. When dissolved in water it releases substantial amounts of heat, which may prove sufficient to ignite combustible materials. Sodium hydroxide is highly corrosive. Sodium hydroxide is generally used as a solid or a diluted in a 50% solution. This chemical is used to manufacture soaps, rayon, paper, explosives, dyestuffs, and petroleum products. It is also used in processing cotton fabric, laundering and bleaching, metal cleaning and processing, oxide coating, electroplating, and electrolytic extracting. It is commonly found in commercial drain/ oven cleaners.

Potassium Nitrate
Potassium Nitrate is a crystalline salt, KNO3; a strong oxidizer used especially in making gunpowder, as a fertilizer, and in medicine. Potassium nitrate appears as a white to dirty gray crystalline solid. Water soluble. Noncombustible, but accelerates the burning of combustible materials.

more to come...

 

[PeteC]

Welll... there should be lots of surplus PPE on the market soon,

 

[stansdds]

Hot Caustic Bluing



I CAN NOT STRESS ENOUGH HOW IMPORTANT IS THE PERSONAL PROTECTION EQUIPMENT WHEN DOING THIS: CHEMICAL GLOVES, RESPIRATOR, FACE MASK, LONG SLEVES, CLOSED SHOES, LONG PANTS AND APPRON IS THE MINIMAL PROTECTION GEAR THAT YOU SHOULD WEAR. THIS THREAD IS FOR INFORMATIONAL POURPOSES ONLY. IF YOU DECIDE TO DO THIS, YOU DO IT AT YOUR OWN RISK.

Personal Protection Equipment you should wear


First aid information worth reading just in case: Chemical burns: First aid - Mayo Clinic


Setting your expectations: It is very likely that initial results will not be outstanding. If you are looking for fast and outstanding result, perhaps you should consider sending your slide to a qualified gunsmith.

So does you think I be ok usin' mah wife's kitchen gloves, corony-virus mask, mah WalMart sunglasses, mah Bon Jovi T-shirt, mah cut-off jeans, an' mah flip-flops fer mah pee-pee-eeeeee?



Seriously, this is a hazardous process, one mistake is all it takes to ruin your day or ruin your life. Beware and heed the cautions.

 

[guzzitaco]

Hardware & equipment

Hardware

Container or tank: you will need a container for the bath. Commercial tanks are a bit expensive but are large enough to fit a rifle/shotgun barrel. Since I only blue slides and small parts and we are discussing a “home” setup, I used a pot.

Pot can made of steel (avoid stainless-steel since it can leave mark on the parts). It must be large enough to fit the part suspended in the solution, without touching the sides of the bottom (if parts sit of the bottom they will develop a reddish spot that will stay and the finish will not be even). The steel pot CAN NOT have aluminum rivets for the handles. The solution WILL MELT the aluminum rivets creating a hazardous situation.

Another alternative is to use a ceramic coated pot, like the ones sold at Walmart. They will run for about $15 to $20.



Please remember, you cannot use an aluminum pot because it will MELT.

If you are going to use an old pot, you MUST wash it very well and remove ALL grease (use a degreaser like TSP). If you cannot remove all the grease, you cannot use it. Once the pot has been used for the caustic solution you can never use it for cooking again. NEVER.

Thermometer:
You will need a stainless-steel thermometer and that reach up to 350 deg. It must be long enough to reach the bottom of the pan. No, you cannot use an aluminum thermometer because it will melt. You can find one for around $15



Stirring rod:
You will need a large spoon or a stirring rod. I use a large stainless-steel spoon that I have (and never used) from an old BBQ set. Some people use a glass rod (large and strong enough). Do not use wood, it could react with the caustic solution.

Heat Source:
You need a stove gas or electric, large enough that your pan can sit on it and powerful enough that can boil water. Your stove must be leveled; sturdy and stable to prevent any kind of accidents and to let you work comfortably. Some people use a camping stove or an outdoor burner.

Place to work:
You cannot do this in your kitchen or inside your home. Fumes are corrosive. It is simply too dangerous. Working area must be ventilated and well illuminated. You need space to move around without stumbling with boxes and you will need a place to sit. You will also need access to running water in case of an accident. A fire extinguisher on hand is also a good idea.

Other things you will need: A table next to the heat source, where you can work (I don't like putting things or working on the floor). And a timer.

What I use:
I have an old stainless-steel pot. It is not too big, but big enough for a slide and some parts. I have a stainless-steel spoon (BBQ) and a stainless-steel kitchen thermometer (the wife had 2 so I stole one). My heat source is a Weber grill that has a side burner. My house has a detached garage, that is where I set the bluing bath. I have enough space to move around comfortably. I have a water hose ready and an extinguisher nearby. I use my phone’s timer and camera.



more to come...

 

[skjos]

A lot to take in, I have a stainless turkey cooker, but the handles appear to be aluminum and I use it to cook deep fried goodies, so I would need to purchase a dedicated container, thermometer, and stirring rod. I'm looking pretty good on the PPE.

 

[guzzitaco]

A lot to take in, I have a stainless turkey cooker, but the handles appear to be aluminum and I use it to cook deep fried goodies, so I would need to purchase a dedicated container, thermometer, and stirring rod. I'm looking pretty good on the PPE.

The pot I use is not big, it is only 4 quarts = 128 oz.

Since I wanted to leave 1 1/2 to 2 inches of space from the top because the formula boils...my max working volume of solution is = 114 oz

I avoided a large pot, because I didn't want to mix that more formula. I was concerned enough with the caustic reaction, so didn't wanted to mix a lot of it. Also, it is more expensive to run bigger batches.

 

[PeteC]

Awesome thread and information. Btw, cheap old stainless steel pots can sometimes be found at Goodwill, garage sales,... because most people don't use the 6 -quart size that used to come with sets. I have an extra one came from there, and the old plastic handles are removable with a Phillips screwdriver.

(Now if Goodwill just started selling some cheap old stainless steel firearms.... )

 

[guzzitaco]

Commercial products

Commercial Salts
Before attempting to mix salts in a formula, I decided to investigate what was available in the market.

Brownells (not affiliated with them) offers bluing salts that gunsmiths have been using for years. The store is well known for the quality of the products they sell and its customer service. The problem that I had was that the size of the container was huge…40-pound pail !!!…that was enough to do all the slides I wanted to do in three lifetimes!!! I needed a different option.

There is another company called EPI that sells a product called Ultra Blak 400 …the product and the company have an excellent reputation. They even have a variation that is in a liquid form, so you don’t even have to mix it. The problem here is that the shipping cost was skyrocket high because the product is considered hazardous. Unfortunately, this wasn’t an option for me either, since I was learning and wasn’t ready to invest a lot (plus we were in the middle of quarantine and I wasn’t generating any income). The company has great videos of their products on youtube.

There are a couple of other interesting videos in youtube for you to see. Neither videos display good safety protocol (PPE is not being used, one of the guys is wearing flip flops), also there is not clear temp control to time control, so please do not use this as an example of HOW to do this, but they will give you an idea of the process, how the solutions boil and a snapshot of the results…(I suggest you turn the volume OFF in the first one, music isn't great)

[ame]https://www.youtube.com/watch?v=5dD2whqXzQM[/ame]

[ame]https://www.youtube.com/watch?v=wAd1hNO-iuY[/ame]

Both videos use an electric fryer as a heat source and as a tank...I think is a great idea, unfortunately I don't have one I could use (my wife gave me the look when I suggested it...)


I found some other commercial products, but at this stage I was ready to mix my own salts.

more to come...

 

[guzzitaco]

Clarification

Clarification on tanks (Pots) and stirring rods materials

I’ve gotten a couple of questions on this, so I think it would be good to clarify.

The solution tanks must be steel or ceramic coated. Soldered or brazed seams will dissolve, ruining solution, tanks, and whatever gets leaked on. (AVOID STAINLESS-STEEL, IT CAN LEAVE MARKS ON THE PARTS !!!)

The solution slowly attacks glass when very hot but at room temperature it can stirred with a glass rod. So, before applying heat you can use a glass rod to stir the solution but after you apply heat, you shouldn’t use glass.

 

[guzzitaco]

Formula

As with any recipe, there are many of hot bluing formulas. Most gunsmiths have their own touch or twist…like a secret sauce…

However, I think many of them derive from Roy Dunlap gunsmithing book (found on page 399 of NRA published copy).

Dunlap attributes this formula to Don Lowery and says this produces an unbelievably durable finish that can take a wire brush test without damage. I have tested this, it is strong but it is NOT Melonite, it will wear off, but in my opinion it is more durable that other factory bluings I have seen.


The Formula:
5 pounds lye
2 1/2 pounds potassium nitrate
per gallon of DISTILLED water


Calculating formula by weight:
1 gallon of distilled water = 8.3 pounds
5 pounds of lye
2.5 pounds of potassium nitrate
total = 15.8 pounds

By Percentage
distilled water = 52.53%
lye = 31.6%
potassium nitrate = 15.8%

I use a small kitchen scale to measure everything. Keep the proportions and adapt it to the container size you are using.

For example I use a 4Q stainless-steel pot = 128 F Oz. You must leave 1 ½ to 2 inches of space from the top of the pot, so the solution has room to boil without spilling over (causing a safety hazard). I estimated my max working volume at approx. 100 F Oz.

1bl= 16 fl Oz

52.53% of 100 F Oz. = 52.53 = 53 Oz of distilled water = 3.31 pounds of distilled water
31.6% of 100FOz. = 31.6 Oz of lye = 1.97pounds of lye = 2 pounds of lye
15.8% of 100 f Oz. = 15.8 Oz of potassium nitrate = 1 pound of potassium nitrate.
Total solution = 101 Fl oz = 6.31 pounds

I have use rounded figures therefore there is a small rounding error.

Apply the percentages to you max working volume. I calculated my max working volume in a very easy way. I took a 20 Oz container and filled it with water…I used ti to fill my pot until I had 2 inches from the top. 5 containers to fill = 100 Oz.

Note: Please check my calculations, I am human and make mistakes (I make a lot of mistakes, more than most humans )

Materials:

Lye (please read definition in post #7)



I buy the lye at Walmart. Cost is $5 per pound

You may use other brands but make sure that is 100% lye and that is does not contain aluminum shavings in it. Also, you can buy pure lye online (maybe around $2 a pound), but shipping may be expensive.

Potassium Nitrate (please read definition in post #7)



I buy the potassium nitrate at Lowes. Cost is $6 per pound

You may use other brands but make sure that is 100% potassium nitrate.

Distilled Water:



I buy the distilled water at Walmart. Cost is $0.78 per gallon.

Cost to run a batch on bluing solution:
So, using a 4q stainless-steel pot, I need:

2 points of lye = $10
1 pound of potassium nitrate = $6
1 gallon of distilled water = $0.78

Total = $17. Plus the propane you consume on your heat source...

more to come...

 

[guzzitaco]

Bath operation

How the bath works:

Pour the distilled water into the pot. SLOWLY add the sodium hydroxide (lye) to the distilled water while stirring. The mixing will begin an exothermic reaction that will raise the temperature to around 240 F Deg. Once thoroughly mixed, slowly add the potassium nitrate.
Continue stirring. When everything is mixed, turn on the burner (mid temp to start with) and heat the mix to 285-295 F a that temp you can put the parts inside the bath.

The solution must be kept at a constant boiling between 285-296 deg F. (No boiling, no reaction, no bluing)

The tough part is to keep the temp at 285 -295 F. The solution contains water at around 50%, water boils and evaporates at 212…so, at 295 the solution is evaporating water (consuming water) to keep the reaction going. As water evaporates the temperature starts to increase, but the bath only is “effective” between 285 and 295 deg. So, you must control the temperature and maintain it at the 285-295 rage for the bluing process to be effective.

Larger bath has more water, but same range temperature, so they have more water to “burn” before you need to add more water.

Smaller baths at the same temp, have less water to “burn”, so they will tend to increase temp faster.

The problem is to keep the temp between 285 to 295.

To reduce the temp, after the increase caused by water evaporation, you have 2 options: add more water or reduce the heat.

Once you reduce the heat the boiling stops. When the boing stops, the reaction stops. So, the bluing stops. (I made this mistake the first time I did the process, resulting in a brown part).

Depending on your tank size you may have to add more water. Adding water to a hot caustic solution is VERY DANGEROUS. Water must be added very SLOWLY, VERY SLOWLY.

A large amount of water, violently added to the solution is DANGEROUS it will generate a boil over and can cause a steam eruption that could burn you. Add water slowly very slowly. I start to add water as soon as the temp reaches 290. You will see the level of the bath decrease, then it is time to add water. (Be extra careful in doing this and make sure to wear your PPE)

In the video below you can see how water is added to a Caustic solution (the person doing it should be wearing chemical gloves, but I think it is important to see the water reacting to the solution). Minute 1:02 adding water.

[ame]https://www.youtube.com/watch?v=K5lvnTKcMeE&t=2s[/ame]

A safer method to add water is to turn off the heat, let the solution cool down and then add water. However, this will make the process longer, much longer.

Another alternative is to mix more bluing solution, before starting, and keep the spare solution handy adding it the main solution as it dries up.

What I do:
I run a small tank (pot), water evaporates every 15 minutes (approx.) and the solution starts to get above 295. I add water slowly. I wear all the PPE and try to keep a distance. I have to add water 3 to 5 times in the 45 to 50 min the process takes.

A good idea is to use a lab safety bottle, so you can keep more distance while adding water.



A bottle like this costs $7 at Grainger. It is a good investment.


more to come...

 

[JohnHL]

Maybe I'm over complicating this, Guzzi, but would it be safer to add small amounts of boiling water?

John?

 

[guzzitaco]

Maybe I'm over complicating this, Guzzi, but would it be safer to add small amounts of boiling water?

John?

Hi John,

I honestly don't know, maybe the reaction would be less "violent" if the water is hot but I am not sure.

I think the problem with the water is due to the caustic reaction itself, where the lye (sodium hydroxide) generates a reaction when it interacts with water. Maybe warm or hot water, would make the reactions less violent, but there will be a reaction...

As I read it in another forum: ("Add water . . ." Such a simple statment. Adding water to a working blueing bath is a bit like adding water to the working lead pot. Neither the bath nor the water like it!) (I guess it's like me at my in-laws Xmas dinner )

The only "safer" way to add more "liquid" that I have found (reading) is to add more bluing solution. So, you would have to mix extra bluing solution and use it to re-fill the one that is evaporating...however, my concern would be the higher saturation of salts...

I am sorry I don't have a better answer at this point...

 

[Dieseltech56]

I’ve been wanting to try home bluing for some time now but I was turned off by the cost and volume of the solutions at brownells. This is honestly the info I’ve been looking for