Coating For Mild Steel

Here's what I use.

http://www.brownells.com/gunsmith-t...-chemicals/oxpho-blue--prod1072.aspx?psize=96

This is also sold by Birchwood Technologies under the name "Presto- Black". Used to be called "Tool Black" and may still be called that when bought at certain tool houses that would carry the stuff.

https://www.birchwoodtechnologies.com/store/Room-Temperature-Blackening-for-Iron-and-Steel.html

A couple of things to remember, degrease the parts. I go borrow a little Dawn dish washing soap from the kitchen. Use hot water to wash and rinse the parts off with. Do this wearing HF disposable gloves so you don't get finger prints on the parts from your oily hands. While the part is still fairly warm, head for the garage and start to applying the blackening solution using shotgun bore wipes or cotton balls. It should turn black instantly. After about 20 minutes, wipe off parts with paper towels and oil. DO USE WD-40! Steels with a high Chrome content may not coat evenly or coat at all. I've had this to happen, too. High hardness with high Chrome content like in some of the 4140-4145, 4340 materials may not coat very good. Heat in the parts does help, say 180-220 degrees F. Just a few pointers I've experienced in the past using this stuff.

Until about six months ago, I had a local source that did manganese phosphate coating which we use extensively for down oilfield equipment. What little stuff I needed done, they would do it for me. In exchange, I usually ground up special cutting tools for them in trade.

Ken
 
I get it from pottery suppliers in bulk. Cheap. It's used in coloring ceramics. Fairly pure that way and already powdered. I have a heated stir plate and get my acid up to about 200°f and run about 10-12% by weight and cover. Sit heated for 30 mins min, then after cooling, pour off the top. What settles is excess to a saturated manganese phosphate solution. The reaction rids itself of the oxygen, if I remember my chemistry right. This I dilute about 30:1 with destilled or DI water for critical stuff, or in my bigger containers (60 gals of so) I just use tap water. It does make a difference, but on the larger parts seldom is it all that critical that it comes out perfect.
 
Nothing encourages rust like HCl (muriatic acid). Phosphoric provides a pretty good base for paint and discourages rust.
Hydrochloric is what I use before painting chrome. I also use it for mild steel at times. That fast rusting is why I think it works so well to hold paint to chrome.
I add manganese dioxide to my phosphoric acid. Therefore I get something akin to KemPlate from the old days. Big Red spec'd it, as did most of the oilfield service companies.

I get it from pottery suppliers in bulk. Cheap. It's used in coloring ceramics. Fairly pure that way and already powdered. I have a heated stir plate and get my acid up to about 200°f and run about 10-12% by weight and cover. Sit heated for 30 mins min, then after cooling, pour off the top. What settles is excess to a saturated manganese phosphate solution. The reaction rids itself of the oxygen, if I remember my chemistry right. This I dilute about 30:1 with destilled or DI water for critical stuff, or in my bigger containers (60 gals of so) I just use tap water. It does make a difference, but on the larger parts seldom is it all that critical that it comes out perfect.
Thanks Tony.
I copied that to a word doc for future reference.
 
I get [manganese dioxide] from pottery suppliers in bulk.
I'll buy some if I ever start doing a lot of phosphating. In the meantime dead batteries are free (the stuff in dead ones is actually Mn2O3 but seems to work fine. It's also very finely powdered).
 
John,

I'm going to try your mix one day. Have plenty of dead alkaline batteries daily around here. Have plenty of muriatic acid from the swimming pool, too.

Ken
 
John,

I'm going to try your mix one day. Have plenty of dead alkaline batteries daily around here. Have plenty of muriatic acid from the swimming pool, too.

Ken
I use phosphoric acid, not muriatic acid. Muriatic acid is good for stripping steel down to bright metal but that bright surface will rust while you are looking at it and needs some sort of paint or treatment promptly.

I also use phorphoric acid to remove rust. It's slower than muriatic acid but less agressive. It won't dissolve the metal and change dimensions and it leaves a rust-resistant surface.

Also note that my slapdash process does not produce a consistent firearm-quality coating. You may get blotches and variation from one part to the next even in the same bath. It's for corrosion reduction, not appearance. If you need a really pretty finish read up on parkerizing.
 
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Good point John, your right on the phosphoric acid.
Thanks, Ken
 
I use the same product from Caswell, been pleased with the results.

Greg
 
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