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Fed up with the usual proprietary cold blue offerings and their lack lustre results I ventured forth onto the Internet and picked out the simplest recipe for home brew hot bluing that I could find.
Essentially it's 500g of caustic soda dissolved into 1 litre of distilled water then slowly heated to the boil whilst gradually adding 500g of sodium nitrate whilst stirring with a wooden spatula to thoroughly dissolve.
When happily boiling away gently lower in the part to blue and leave for twenty minutes. Stir solution every now and then.

This stuff is toxic and extremely caustic to the skin so obviously wear a suitable pair of protective googles, a suitable mask, and stout rubber gloves. Have plenty of water about to neutralize spillages.
Do it outside - the fumes are toxic and will stink out your garage - not to mention corrode anything metal nearby. All the usual disclaimers. Keep pets and kids out of the way.

Remove the part and thoroughly clean with boiling water. Go nuts with the WD40 afterwards to drive out any moisture. I was really impressed with the end result - far bluer than any cold blue product I've ever used and totally even throughout. It almost matches (but not quite) the factory blue on the barrel. The barrel has a certain sheen that is hard to replicate - but you'll have to stare hard to see the difference.

Let the solution cool and then you can pour it into a suitable plastic container for reuse - don't forget to mark it up as poisonous and caustic.

Preparation is everything - I boiled the cylinder in white vinegar and removed the existing remains of bluing with a stiff paint brush until it came out bare metal. Instead of washing with boiling water (causing it to instantly stain brown with rust) I thoroughly washed out the vinegar with carburretor cleaner , let if flash dry, then put in the bluing solution.













I used a cheap gas camping stove for heat. I mixed up the solution in a pyrex dish - a steel tub would have been better - less likely to get tished. You can neutralize the mix with vinegar but it causes an exothermic reaction - so you don't want to do it on flesh.

That sounds like something even a numpty like me could do, which is probably a good reason not to! Thanks for the info!

Les wrote:That sounds like something even a numpty like me could do, which is probably a good reason not to! Thanks for the info!

I was filled with the appropriate concern when I did it too. :)

BTW - I couldn't do it on my cylinder as it has a reproduction of the Colt engraving on it (didn't want to rub out the detailing) but it'd be worth polishing up with fine wire wool before dunking it in the bluing solution for a nicer finish.

i used this method 30 years ago in a company laboratory with a glass screen between me and the solution. This stuff is dangerous---it can spit when the nitrate is added. I was taught to boil up the caustic soda and then gradually add the nitrate, checking each time with a slip of steel. Add nitrate---check---instant red rust--- add nitrate---check---instant red rust---add nitrate---check---instant dark blue.
Do not do this in your kitchen.
Fred

FredB wrote:i used this method 30 years ago in a company laboratory with a glass screen between me and the solution. This stuff is dangerous---it can spit when the nitrate is added. I was taught to boil up the caustic soda and then gradually add the nitrate, checking each time with a slip of steel. Add nitrate---check---instant red rust--- add nitrate---check---instant red rust---add nitrate---check---instant dark blue.
Do not do this in your kitchen.
Fred

I had expected it to spit a bit and was a bit nervous of adding the nitrate to the caustic brew. From my dim memories of school chemistry I managed to retain the notion that you add acid to water - not the other way round because of the risk of splashing. The same principle ought to apply here you would think (although it's a strong alkali rather than acid). However, the recipe called for it in this order and I assumed it mattered. Chemistry is not my strong point. Sodium nitrate though is harmless - it's used to preserve some meats. If it didn't matter it'd be more sensible to boil the sodium nitrate solution first and then add the caustic soda.

There was nothing so sophisticated in my process as checking for stages at which to add the nitrate. I put the lot in, boiled it, added the part to be blued and was hugely pleased that it worked right off the bat.

The original recipe called for a lot more of all the ingredients - we're talking almost two gallons of end solution. I simply scaled it down in direct proportion and went with it. I was suitably wary of Mr Cockup riding into town so did everything very gingerly and at arm's length - and, unusually for me, I wore all the proper safety gear. Also old clothes and long sleeves are a good idea.

having done a bit of research on the topic of bluing myself recently it appears there's a huge number of ways to replicate / create a blue finish using household items. One chap on YouTube used tree stump remover. Another fellow over here heated up a metal part and dipped it in used motor oil. Whilst these aren't as good as a professional finish they are considerably cheaper and the results looked pretty good.

Well done on yours, it looks to match quite well.

JS569 wrote:having done a bit of research on the topic of bluing myself recently it appears there's a huge number of ways to replicate / create a blue finish using household items. One chap on YouTube used tree stump remover. Another fellow over here heated up a metal part and dipped it in used motor oil. Whilst these aren't as good as a professional finish they are considerably cheaper and the results looked pretty good.

Well done on yours, it looks to match quite well.

Cheers.
I've seen, and considered, those too. In the end it boiled down to the cheapest / easiest to get materials and the simplest instructions.

I think if I were to do the job over I'd take the time to make up a wooden box with a perspex front for extra safety - not to mention keeping the fumes going upwards instead of wafting wherever I seemed to be standing. Also this would prevent the gas flame being blown out a few times due to the occasional sudden gust of wind.

It certainly worked better than I expected and much better than my usual experiences with cold blue.
Having said that I once managed, with extreme diligence and preparation, to get an extremely good finish on a Mosin Nagant barrel using G96. So good in fact that you would be hard pressed to see that it wasn't original. It was a result I've never ever been able to achieve with cold blue since.