Quote:
Originally Posted by alvin
I have never done things like this before. From youtube.com video, midwayusa showed how -- the nitre blue salt is a pink color solid stuff, he put the salt into a pan and "cook" it. The salt melted. Then, he dipped small parts into the melted salt, the metal color changed, then he took it out. That's it.
He did not explain the theory. Here is my guess -- that salt melts around 600F. So it's just temperature control media. This is obviously more controllable than using a torch to create fire blue on small parts -- using torch, you have no control on temperature, using this type of salt, it's much easier to control, and the metal is heated much more uniformly. Unlike regular bluing process, I don't think there is a chemical reaction between the nitre salt and metal. Just a guess.
Here is the video:
https://www.youtube.com/watch?v=-vF3zKiUIkY |
That's correct. The nitre salt is just a media that allows you to apply the heat in a controlled manner, otherwise it's the same process and the same finish as you'd get with a torch or in the oven.
One reason why I don't use nitre salt (and bluing salt) is that I don't like the idea of working with salt heated to high temperatures. I figure it can make for some interesting steam explosions if there's rinse water left on the parts. Still, many videos show the guy dipping in the nitre bath, dipping in a cup of water, then back to the salt again etc. I might be overly cautious, but I figure the torch and the oven are much safer.
I do extractors on a thin piece of shim stock, I heat with a torch from underneath and when I have the right color I drop it in quenching oil to cool off. The color doesn't appear immediately and it can continue to develop after you quit torching the part, but the quenching will stop the process right at the moment it's submerged and keep it at the right color.