Bluing help

[Dominion22]

Need some help with my bluing salts. Using a homemade recipe with caustic soda (23#), sodium nitrate(9#), and sodium nitrite(3#). Everything was going good then salts started to foam instead of boil, at any temp. Change out the batch and went to a 2:1 mixture of caustic soda and sodium nitrate. Same result. Any help or ideas would be greatly appreciated

 

[GGaskill]

Are you using a thermometer? What were the temps?

 

[Dominion22]

yes I have a thermometer. Started foaming at 260F. Added some caustic soda to bring temp to 285F. Have to shut off the flame to keep from foaming over. Parts blue fine

 

[wyop]

Is there any aluminum involved in all of this? Are you mixing or measuring your salts in aluminum pans?

 

[Dominion22]

No aluminum anywhere.

 

[Dominion22]

Measure and mix salts in plastic pails

 

[1yesca]

there are as meany homemade recipe is there are people that blue some work and some don't . if you like the finish then stick with it just may need a bit of tinkering here and there with the mixture or method also there are some recipes in dunlops book of gunsmithing you mite want to cheek out

 

[GGaskill]

Have to shut off the flame to keep from foaming over.

Maybe you have the tank too full.

 

[john.k]

More likely the solution is a slurry of crystals,that provide foci for boiling.......add more water (carefully)

 

[gwelo62]

I worked with a former RN armourer. He used 50/50 ammonium nitrate and potassium nitrate melted in a steel tank made from a piece of channel. Cyanide was addded if bluing cast steel.

 

[john.k]

When the solution suddenly boils over,its caused by a superheated solution.....beyond its normal boiling point

 

[Dominion22]

How does it go past boiling to superheated ? In the past once it started boiling it just stayed there , needed water every so often to keep temp down. I could turn the flame down to keep it at a low boil. Not sure what changed , I changed the salts out and started fresh with the same results. I’ve added water to get temp down to about 250 and still foams

 

[john.k]

usual cure for foaming is mechanical stirring of the solution .

 

[JohnMartin]

Superheating is sort of like supercooling, or supersaturation. Sometimes it takes a little “nudge” to get the bubble or crystal to form. Stirring often does it.