Questions about Blueing

[SHostetler]

I've been reading about the different blueing processes and have become thoroughly confused. Could someone please explain the differences between heat blueing (pretty obvious), gun blueing, cold blueing (again pretty obvious) Nitre blueing, high temp salts, low temp salts, and water soluable salts?

Is the surface penetration better with one or another? Do they give a different range of colors? Any other tidbits of trivia about the processes would be appreciated.

Thanks
Steve Hostetler

[Ed Caffrey]

Bluing basically falls into one of two catgories....

Heat bluing: oxide color produced through temprature.

Chemical Bluing: colors produced through a chemical reaction.


Heat bluing would include any method that produces the color(s) by exposing the workpiece to temprature. IE: Heating in an oven

Chemical bluing is where the workpiece is exposed to a chemical that reacts with the workpiece material and produces a color. IE: Nitre blue, or commonly know gun (hot) bluing. This method also includes the cold blue formulas.


You can achieve a wide range of colors with both heat bluing, and with Nitre Blue. Gun bluing salts (hot type) are very limited on the colors they achieve, as are cold bluing solutions.


As far as durability, none are extremely durable. I would have to say that heat coloring is the most fragile of the lot, and can easily be scratched or worn off. Gun bluing salts is likely the most durable, but you are restricted to a very deep blue/black color with most of those.

My overall choice is Nitre Blue. It is more durable than either heat coloring, or cold bluing solutions, and with Nitre Blue you can achieve a fairly wide range of colors.

Any time you plan on coloring a guard/blade/buttcap, or whatever else, the devil is in the details. Various shades and brilliance levels are obtained with different finishes prior to coloring the workpiece. A mirror polished workpiece will yield the most brillant colors, with the colors becoming more pastel as the finish declines. One of my favorite finishes is to mirror polish a bowie guard, then take it to a very fine carding wheel mounted on my buffer. This produces a very fine "orange peel" texture, and gives the color a slightly pastel look without being too "girly".

[jdm61]

My VERY limited experience with cold blueing solution is that it will stick ok to low carbon fittings steel like 1018, but the blade steel that i tried it one (O1 and 5160, which both contain chromium..no clue if there is a connection) came out very uneven and the finish was quite fragile. It rubbed off very easily. Ed...what is the diff between nitre blue and regular hot blueing salts?

[Ed Caffrey]

The regular hot bluing (the type used on firearms) is a mixture of caustic salts and water. The mixture must be fairly precise to work correctly, and in my experience are very messy to work with. About the only color you can achieve with this type of bluing in the deep blue/black that you see on most firearms.

Nitre Blue comes in a crystal form, in a plastic bucket. You DO NOT add anything to it. Place it in a metal steel pot/container (I try to avoid using aluminum or cast iron) and heat it. The crystals melt a about 300F (change to liquid), and the part that you wish to blue/color is dipped in and allowed to soak for a while. The instructions with Nitre Blue recommends that the liquid be at 570-650F to achieve the brilliant blues associated with this media. I don't think I'd be doing it on the kitchen stove, but some do. A coleman stove or other camp type stove works great for heating it.

The good thing about Nitre Blue is that when it cools, it changes back to a solid, so you don't have to worry about anything getting sloshed around and spilled when your not using it. I also use it for the low temp side of molten salt heat treating.
The colors you can achieve with Nitre Blue are much wider than with regular firearms bluing salts. Just about any color that one would normally see from straw to sky blue can be had with it.

[jdm61]

hmmm.....could you temper the blade using the nitre blue salts? Also, how do you case harden? i always see it referred to as using bone and charcoal.

[mete]

Yes you can temper in the salts. There are processes that use salt for carburizing and nitriding .The carbonitriding is for thin case and uses cyanide salts .This is not for amateurs - cyanide + acid = hydrogen cyanide [as in the gas chamber !! ]

[Ed Caffrey]

The method for using the high and low temp salts for heat treating is very straight forward. The high temp salts is mearly the heat source to achieve austinizing heat, then the low temp salts are the quench media. You can also get into doing marquenching where you form banite, however this requires your equipment to be setup so that it maintains the low temp evenly for a long period of time (several hours)

Jon Christensen is the man to answer the questions on case hardening. He does it better and more often than anyone else I know.

Jon.....if you read this chime in and help us out with the case hardening thing!