[Jeremy Lindley]

I've seen on different forums and pictures where makers hot blue their blades and/or fittings. I see it particularly with damascus and understand that it can aid in the contrast of dark to light in the steel's patterns. That being said, I'm not really sure how hot bluing is done... Is there a particular way it must be done and how durable is it? Can it be marred or damaged if contacted with particular materials? If part of the steel that is blued gets messed up, can it be re-done later or touched up or would that only be possible in a take-down assembly knife? Is it primarily only used for damascus or does anyone find it useful on other steels? Does it give better results on some steels and not on others?

Sorry for the litany of questions, just trying to understand the method. Thanks for any help on this.


Jeremy

[Karl B. Andersen]

Jeremy, the hot-bluing I do, and have been doing steadily for 10 years, is one of the popular bluing methods used across the firearm industry.
You own any guns, Jeremy?
It's just as durable as that, because, well, it's the same thing.
When a blade is hot-blued, the entire blade comes out black, then the bluing is sanded off of the nickel bearing layers, as they remain just a little higher than the tool steel layer after etching. That's how the contrast is achieved.
The salts used are extremely caustic and even slightly dangerous, as the salt bath is maintained at around 300. The cleaned parts are submerged in the molten salts for about 1/2 hour and then followed with hot water and oil baths to clean and protect the fresh finish.

That is the basic bluing outline.

Fittings of Damascus and non-stainless steels, blued by the same process, are very beautiful and well worth the effort.

Please take a cruise through my web site and see the different results attainable.

[Jeremy Lindley]

Karl-

Thank you for the reply. It was actually several of your knives (that I rather enjoy staring at for long periods of time) that got me thinking about this. I am familiar with the bluing on guns, but I must say I never thought about how it was actually done. You mentioned a hot salt bath-is the bluing achieved as a result of the reaction with the salt or is there some kind of liquid or other substance that is the bluing agent? Sorry for the dumb follow-up question, I guess for some reason I always just assumed the bluing was some kind of liquid that the steel was submerged in. Anyway, thanks again.


Jeremy

[Karl B. Andersen]

Jeremy, the bluing is a controlled oxidation - basically rust! - as a result of the steel being attacked by the molten salt.
"Salt" is a term used lightly here, it's not your salt that you use on your french fries. It is chemically classified as a "salt". The only other element involved is H2O - water.
The salts are expensive and must be shipped Haz Mat.

[Jeremy Lindley]

Thanks, Karl.

[Kevin Menard]

Karl,

What about other techniques like the black oxide coatings? I've used those on tools and the baths, while a bit toxic, are at least room temperature. Is the hot blue that much better? I've never tried it mainly because of the need for temperature control.

Kevin

[Gabriel Ables]

I've been researching bluing a bunch lately as I prepare to get into it. I have used cold bluing solutions with some luck. Cold bluing might allow easier matching of a touch up down the road. The caustic hot bluing is supposed to be more durable than the cold process. I watched a gunsmithing video recently and rust bluing was also shown. Rust bluing, which is a black blue when done, does not require the investment in salts and temperature control like hot bluing. It does require some moisture and temp control of the environment as it sits and a soft wire "carding" wheel. Some people have to make a "sweat box" to keep better control of heat (70-90f), moisture and air circulation. I will probably try both. Rust bluing is supposed to be more durable but is very time consuming. It seems that bluing fittings could take 1-2 weeks with the rust process. Brownells is a good resource for all of the hot, cold and rust bluing chemicals and instructions. I got the videos off of Smartflix.

My initial shopping list for getting into hot bluing calls for: stainless thermometer, 2 small iron tanks that I will use on a 2 burner coleman stove, small parts basket, cleaner/degreaser, bluing salts, water displacement oil, chemical gloves.

[Brian Thie]

Gabriel

Rust Bluing will produce a great finish, but it is time consuming. A sweat box can be something as simple as hanging the parts in the bathroom while you take a shower, but some form of generating a warm moist enviornment will greatly speed up the process.

For hot bluing, if you are using a coleman stove that is propane, get a converter to hook it up to a 20 pound tank. The 1 pound bottles get cold quickly which reduces the output and you wont be able to maintain the temperature you need. Even with the small tanks, it is going to take some time to get up to temperature.

Get a face shield as well. Hot bluing can be a bit explosive at times --especially if water is added incorrectly.

Brian

[Russell Roosevelt]

Karl and Brian

I'm considering doing some hot blueing, on some knives, and want to know how you deal with the caustic atmosphere it creates?
How do you store the salts and equipment so it doesn't rust everything in your shop.
I have had experience with muratic acid, it will rust equipment in your shop with it in sealed containers.

Russell

[Brian Thie]

Russell

I do bluing outside. It may be a bit of a pain to do so, but that way it keeps things in good shape in the shop. I store bluing in a tank with a lid that has a seal on it much like what Brownells sells.


Brian

[Russell Roosevelt]

Brian

The tank you store your bluing in is a different container than your heating and treatment tank, Correct?

Thanks!
Russell

[Brian Thie]

Russell

I store in the same tank that I blue in. I have a lid for my tank.

Brian

[Karl B. Andersen]

Bluing salts don't "rust" things in the shop like evaporating acids do. It really is just a tank of salt water when you're not using it - for lack of a better explanation.
In other words, there are no caustic gases running rampant around the shop.
A cover for your tank is mostly to keep things OUT of the tank - not the salt IN the tank.
When bluing, there is no "caustic atmosphere" other than maybe some spitting and sputtering that would emit droplets of caustic salt in the immediate bluing area.
I do mine out in the middle of my forge area on the concrete floor.