Homemade Hot Blue Formula
Courtesy of Blair Emory
[my comments in brackets - KM]
All "bluing" is really blacking. The blue shine is due to additional chemicals such as manganese that are added to the mix. They are usually less abrasion resistant than blacking and perforce are thinner to give the blue refraction. They are a lot fussier to do and the results vary more than straight blacking on different metal alloys and heat treatment in my experience. I generally use a lye, fertilizer mix that gives the hardest blacking I have ever seen and it so simple anyone can do it, plus the ingredients are available at the hardware store rather than paying UPS hazardous shipment fees.
- The mix ratio is 5 lb lye (sodium hydroxide) to 2 1/2 lb ammonium nitrate (fertilizer), to 1 gallon water.
- Grocery store lye [I use Red Devil] and ammonium nitrate fertilizer (at least 30%). Make sure you are buying actual ammonium nitrate; many brands today are made from urea or some other source. Make sure to not use tap water. Buy distilled.
- If ammonium nitrate is not obtainable, sodium nitrate can be substituted at the same ratio.
- Mix out doors as lots (and I mean LOTS) of ammonia gas evolves and will rot your lungs out if you sniff it. Wear goggles as this stuff foams and bubbles like mad. Very violent exothermic reaction. Mix in a iron pail (not galvanized). [I use a 16qt enameled stock pot.] Once mixed and operating the bath, there is no off gassing, but the vapors are corrosive so don't do it in your gun room or machine shop. Use plenty of ventilation. [I added water first, then added 1lb of lye and alternated with fertilizer. Add slowly to avoid boilover. Also, use a full face shield and a respirator that will filter out ammonia.] After mixing, the solution will be over 100 degrees due to the heat of the reaction.
- Bath operates at 285 to 295 degree F. If you don't have a thermometer, heat until a sample part will just sizzle cold water. [I use a steel deep fry thermometer. Make sure the one you buy will reach the bottom of your pot. I also use a propane deep fryer kit.] Takes 15 to 45 min. depending on the steel and how dense a film you want. [I removed my gun after 20 minutes.]
- Suspend the parts with wire to keep them away from the bottom and sides of the pot. Ideally you want to have a vigorously boiling solution surrounding the parts on all sides. If they get into a hot spot, you will often see red smut on the parts, or it may impart a plum color to the blue. Small parts can be strung together with iron wire or placed into a steel basket.
- After you are done, take parts out, rinse in clean hot water. [I like to have a smaller pot of water near boiling to rinse the parts. This is the best way to wash away the lye, which will begin to congeal as it cools.] Dry and oil. You are ready to go. If you don't like the depth of color after it's dry, (but before you oil it) just put it back in the bath and cook it some more.
- Bath will do 10 to 15 jobs before you have to add about 1 lb lye to a 5 gal bath to make up for boil off. Add water as required to keep the concentrations correct, but this does not seem critical.
- You MUST add enough water at bath cool down, to more than make up for boil off or it will solidify and you can't re-melt easy. If you add too much, I will just boil off next time. [This stuff takes several hours to cool back down. Once it gets hot, it really stays hot.]
- Make sure the parts are clean. Any oil will ruin the bath and job. Boil parts in TSP, Oakite or such first. [I found some TSP at Home Depot. Be sure you have wiped away any water spots, or they will show up under the bluing.]
- Store in glass or plastic jugs between use, if it crystalizes , it is shot.
- You do not have to plug the bore as the magnitite film is harder than the steel and, if anything, should improve it. Possibly a little chemical milling too. I have made test coupons and put them in an open beaker of water for a month with no corrosion. Even light sanding will not break down the surface.