Fertilizer Grade KNO3 as Nitre Blue

[Laredo7mm]

Well, I bought some fertilizer grade potassium nitrate to test out if it would work as Nitre Blue. I bought a 50 lb bag and tested a small bit on the stove top with an old pan. The stuff looks ugly when melted. It started out as white granuals, then turned kinda brownish when melted. Anyway, the trial test on the stove went well, at least i didn't blow up the house. So I threw caution to the wind and dumped the whole bag into a stainless steel pot and stuck the 170,000 BTU propane burner under it.

45 minutes later, it was all melted. I did not buy a high temp thermometer so I don't know what temp it was at. I tried to keep it just melted, probably around 650 deg F. As with the lead (if you all read that post) the salt would solidify and adhere to the steel. But after the steel had a chance to come up to temp, everything was OK.

It took a little trial and error, but what I came up with was a 5 second dunk with a 30 wait between dunks (after the salt stopped sticking) until I got the color i wanted. Once the color was acheived, I quenched it in water.

Anyway, below is my test piece. I buffed off the color from half the piece so you could see the color change better. I think it is kinda neet, but I don't know if there is any advantage doing it this way or just using a torch or HT oven.

Any of your advice on this subject would be greatly appreciated.

 

[itrade]

Thanks for the test Laredo7mm

Dang, I wish you had said that it produced a deep-deep hard finish. Something better than what you get with a torch. But that's the way it goes.

Tonight I built a jig thingy with 1018 and used Oxphoblue to finish it. It was a tad warm and made a dark blue/black finish. After I read your post I ran out to see how deep it was. With 800 grit it comes off as easy as my heat-blue from the lead.

I hope C-Camerer adds in that the commercial stuff does some kinda magic. Maybe he has a few tips too.

Maybe the reason folks used it over a torch was because you can control the heat over a larger area.

Be that as it may, I'll be buying some from the hardware store and using it myself. If it comes out the same as Oxpho without the stink, I'll be using it.

BTW did you get a real variety of colors? That bar doesn't look too bad. I'd like to see something a tad lighter. How many 5 sec dunks was it?

Steve

 

[Laredo7mm]

The colors went through the normal chages, from yellow to blue. I think you are right about this method being more controlled over the entire sample.

I am supposed to be getting the Blue Wonder in on 2/03/03. I will let you know how that works also. Probaly do the sand paper test on it too, just to see if it is more durable than fire bluing.

 

[Alarion]

Nitre blue will blue the steel with a more homogeneous temp than a torch. For the rest it's the same process AFAIK