Rust Blueing Techniques

[Erzulis boat]

I have been doing quite a bit of rust bluing recently, and had to learn most of it the hard way. It is an art, and that automatically reduces the number of individuals willing to share methods. I have used both tap and distilled water, and found that distilled yields better results. Carding with steel wool must be done thoroughly between each swabbing of the solution. Card with light pressure and do it in even strokes. If your carding is done haphazardly and if you allow the rust being removed to remain suspended in the water puddling on the metal's surface, it will show up after the final boil.The final boil is the most important step to do correctly. The instructions will state that clean water must be used, this is true. Change the water for the final boil, even if your heatsource is slow. You must do it. The very nature of rust blueing is an excercise in patience. When you are carding do not be frustrated if it appears that everytime you do it you remove a substantial part of the coloration, the final boil will bring it back. You can achieve fantastic results with about 5 iterations of the boil, apply, boil, and card. Let the parts get hot when in the water, take your time. Try to plug the bore and vent as best as you can, but expect the water to sneak in, it will not destroy anything. The last pistol that I built got invaded, but after the final boil the bore was a fantastic shiny black without a trace of rust. As you can assume I did not swab solution or card the bore, but it blued nevertheless. This reinforces the point of the final boil. If you follow the instructions and use clean water for the final boil, and boil the components for at least 40 minutes, there will not be a trace of rust anywhere, not even on the breechplug threads. A pre-installed stainless steel vent will remain silver and look great. Silver wire inlay on you barrel and lock will also remain bright, but you must card it too, if you neglect to card the silver or stainless steel, it will acquire tarnish spots that require polish to remove, thus ruining your surrounding blue. Anyway, this is not a complete set of instructions for my technique, but these are the ones that will make or break your rust blueing job.

 

[Zonie]

I assume your using some sort of regent to start the rusting?
What, if I may ask are you using? ::

 

[Erzulis boat]

I am using Herters Belgian Blue from Brownells. The instructions printed on the container are woefully lacking. When I first used the regent, I was thinking "Boy, did I get rolled!" But after the second job, everything came out fine. The first time that I did it, it was a total mess. The bluing was satisfactory, but the process was a mess.
The second time was clean and enjoyable. Even a beginner's job if done evenly, will be far superior when it comes to color and character to hot salts bluing.
And, unlike cold blues, rust bluing is super durable, you can treat it just like factory blue.

 

FWIW - Brownell's also sells the Pilkington Rust Blue formula which includes a nice little instuction pamphlet.

Most early browning/blueing recipes are essentially Aqua Regia - a mix of nitric acid and hydrochloric acid - the same base as the commonly used and period correct Aqua Fortis wood reagent/stain. As noted cold/slow/rust bluing, which is an early method, is nothing more than browning the metal and then boiling it in water. The boiling changes the surface oxide from brown to blue/black (it's a chemical reaction that changes the rust from Fe2O3 = ferric oxide to Fe3O4 = ferrous oxide if IIRC).
A point of confusion - cold/slow/rust bluing was commonly referred to as browning during the "period" (and still often is by British arms historians) even though the color was changed to a deep blue/black by boiling. On the other hand the various methods of heat/fire/charcoal bluing were called bluing.
I wonder if the boiling may have originally come about as a way to remove the various neutralizers used? Serendipitously the blue color would have been accomplished.
Slow rust bluing is one of the if not THE traditional method(s) for "coloring" double barreled guns due to the fact that the rib is attached with low heat solder.

BTW - you can also add some baking soda to the water which will aid in neutralizing the reagent used.