Black Oxide Test

pontiac428 said:
I am determined to put together a hot salts bluing setup. Haven't got there yet, because I have no gas burners on hand from other hobbies. Still looking for a free one.

Until that day comes, I have had by far the best results from cold selenium bluing, particularly with Oshpo blue. It is much tougher than the Birchwood Casey equivalent, and much darker. A little bit of heat (just warm to the touch) will kick any chemical process into high gear, so that's a given.
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I recently saw somebody advertising special formulation hot oxide salts that required a lower temperature. A fairly large container (IIRC, 5 or 10lbs) was about $90. Of course I forgot to bookmark it. Will post if I find it again.
 
DavidR8 said:
Hey John, I keep an induction hot plate in the shop for heating up degreasers for the ultrasonic cleaner and I plan to use it to heat up the hot salts bluing mixtures. The first time I ever used it I was stunned at how quickly it boiled water. Like under two minutes to boil a few quarts of water.
Mine has a handy temp setting also so if I need a specific temp I can dial it in.
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KNO3 melts at 633F, and NaNO3 at 586F. Can you use induction heat with a stainless pot? WIll it reach temp? I think the only limit would be the wattage of the appliance. It takes 467 kj/mol to melt the crystal at 586F, or about 250 watts per ounce. If a half hour is a reasonable amount of time to wait, it'll take 8 kw/h per pound. Even if I'm off by a factor of 5, it looks like it will take more energy than a hot plate would put out.
 
MrWhoopee said:
I recently saw somebody advertising special formulation hot oxide salts that required a lower temperature. A fairly large container (IIRC, 5 or 10lbs) was about $90. Of course I forgot to bookmark it. Will post if I find it again.
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Ammonium nitrate has a melt point somewhere around the mid 300's Fahrenheit. I normally don't see the cation as an issue, but ammonium is special. Ammonium can be corrosive, so keep an eye on things.
 
pontiac428 said:
KNO3 melts at 633F, and NaNO3 at 586F. Can you use induction heat with a stainless pot? WIll it reach temp? I think the only limit would be the wattage of the appliance. It takes 467 kj/mol to melt the crystal at 586F, or about 250 watts per ounce. If a half hour is a reasonable amount of time to wait, it'll take 8 kw/h per pound. Even if I'm off by a factor of 5, it looks like it will take more energy than a hot plate would put out.
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It will heat stainless steel.
This is what I have: https://www.nuwavenow.com/shop/pic-gold
 
pontiac428 said:
KNO3 melts at 633F, and NaNO3 at 586F. Can you use induction heat with a stainless pot? WIll it reach temp? I think the only limit would be the wattage of the appliance. It takes 467 kj/mol to melt the crystal at 586F, or about 250 watts per ounce. If a half hour is a reasonable amount of time to wait, it'll take 8 kw/h per pound. Even if I'm off by a factor of 5, it looks like it will take more energy than a hot plate would put out.
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We ran commercial hot oxide at my shop back when. The oxide tank ran about 285-300°F. It was a highly concentrated (720g/l) aqueous solution of a product called Nickel Pentrate, which was mostly lye with some nitrates, a little nickel and other magic stuff.


The lye is present mostly to raise the boiling point to the necessary temperature for formation of black oxide. It requires much less energy than a molten salt bath.
 
I have trying to get stuff ready to try @benmychree 's formula for hot nitre bluing. I have both potassium and sodium nitrate and a small lead melting pot. Not sure what to use for the manganese oxide, as there seems to be quite a few forms of it. Wikipedia indicates there's quite a few forms.
Other manganese oxides include Mn5O8, Mn7O12 and Mn7O13.

Anyone have an idea which manganese oxide is most appropriate?

Curiously, "solar salt" is 60% NaNO3, and 40%KNO3, and is liquid from about 260-550C (500-1022F). I think a eutectic mixture is formed at 45.67% NaNO3 & 54.33% KNO3, but not sure what the melting point is. The 50/50 mix above, is in between. It's apparently ok at 900F (482C).
 
The manganese oxide that I bought and used is Mn02, I bought it online and it was so marked and worked fine. According to the info that I got from the sheet from American Machinist on niter bluing, the 50/50 mixture was the lowest melting mixture of the two salts. Once melted, it will still be slushy at less than 300 deg F. What bluing I have done was at 600 deg. F., for very deep gunmetal finish required by the British and US Government, temps up to 1000Deg F may be necessary, according to the article. In my experience, 600 -650 deg. F gave nice results. Also mentioned is not to leave the articles immersed too long; 5 min. may be sufficient, 10 minutes may be too long with a dirty grey as the result. Also cast iron may be blackened if highly polished, but perhaps 20 minutes may required for good results. This was done on Brown & Sharpe machine handles and was good for rust prevention. I have used the 50/50 mixture for drawing temper at about 1200 deg F, and it seems to be fine, but does a certain amount of fuming.
 
aliva said:
I consider 600-650F hazardous. But that's me.
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I handle 1800* parts from our heat treating oven at work without a second thought.

Hot sticky liquids, that's a hard pass.
 
RaisedByWolves said:
I handle 1800* parts from our heat treating oven at work without a second thought.

Hot sticky liquids, that's a hard pass.
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No big deal, long sleeve shirt, gloves, face shield, about takes care of the potential hazard exposure. It is certainly hot, but not particularly sticky.
 
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