Blueing (blacking) steel

Hi,

In the past there have been various threads about blueing or blacking steel, with people wanting recipes for doing it. Here is one I came across on Youtube.

https://www.youtube.com/watch?v=uh473KIgqjo

The recipe is as follows:

" The recipe i used to make my gun black was:

This method is called hot bluing steel. First you have to boil water with washing soda and put all the parts in it to degrease the gun. Secondly take 1 kg POTASSIUM NITRATE (KNO3) and 1kg CAUSTIC SODA (NaOH) then mix both of them into 1 litter water and boil it. But make sure of your safety first. This is a highly exothermic reaction. So add ingredients slowly and mix them. Put all parts in the recipe then let it boil till you get your desired blue-black color. Apply oil to the parts. "

He shows the process about 8 minutes into the video.

I'm not sure how easy it would be to source potassium nitrate these days ( I got 500g from the local chemist when I was a kid 50 years ago after swearing I wasn't going to make gunpowder - yeah right) and of course be careful when adding the caustic soda to the water (gloves and glasses.

Regards,

Alan

Potassium Nitrate is available as a meat preservative. It is probably on a watch list, and there could be consequences if you order large amounts. As to the method, I don't fancy using boiling solutions containing sodium hydroxide. Call me "chicken" if you wish.

Gloves and glasses, alone, is insufficient PPE when dealing with that concoction. Full face mask and other impervious protective clothing should be employed. I used to dissolve samples in molten KOH or NAOH, then dissolve in hot water for silicate analysis. Not large amounts of reagent, but still required some common sense precautions.

All this is why I use G96 paste and some rubber gloves. It works well enough and doesn't involve heavy kitchen chemistry.

Difference between blueing and blacking. The latter I think is some sort of carburisation leaving a matt black finish.

Blueing involved heating a polished clean steel surface in air so it slowly builds up a thin layer of transparent oxide - the blue colour is created by wavelength-selective reflection from the layer. Applied to watch and clock components and possibly to guns. Nice video from Clickspring here...

**LINK**

Hi,

After a bit of thought I'm sorry I posted this. Even preparing the solution can be hazardous. Adding a kilo of caustic soda to a litre of water will result in a boiling solution which is extremely corrosive to skin, eyes and lungs if the vapour is inhaled.

"Not done it yet" is quite right about the PPE required. The gloves should be heavy duty gauntlet type and a full face visor is essential. No bare skin should be exposed. Both making up the solution and immersing the articles to be blued in the boiling solution should be done outside - not in the kitchen.

Probably best if the moderator deleted my post but I can't find out how to contact him.

Alan

At the risk of being shot down...

I do not agree with you Alan.

This forum seems to be patronised by what I believe ( maybe naively so) at the very least to be intelligent folk. Most have 'health and safety' deeply embedded, and the posters and respondents all point out potential hazards, sometimes to dull repetition even, for the enlightenment of those who 'may' be unaware.

Then information you have provided has some value in itself - it describes a method and process, albeit rudimentary and non-scientific, and maybe dangerous, as are MANY of the things we do. The inquiring minds on this forum , if interested, will research and dig out the do's and don't's, etc.

Your post also prompts posting of other methods and ideas, etc.

I see no reason for you to feel guilty or to obsess about the possible inability of others to behave intelligently on the subject!

It is not on this forum ( nor similar forums) where dire, deathly warnings are always needed, but on the rest of the 'public' internet, eg, Utube, etc - Spend an hour or two and just dig randomly on utube and see what people get up to - I am surprised the world has not been blown up, burnt down or dissolved yet..

Joe

It is all relative. It would not bother me at all as I have dissolved things in boiling aqua regia - a mixture of concentrated nitric and hydrochloric acids. It sometimes took days and one lot of melted material failed to dissolve in such a mixture after boiling for about two weeks! It had far too high a Niobium content in mostly Platinum and should have been melted/granulated with a very large amount of base metal before attempting to dissolve it.

Treating best part of a tonne of turbine blades, first in conc hydrochloric acid to remove any lower soluble metals and then in aqua regia, to recover the gold was another large scale precious metal recovery operation.

When using cyanide powder in the laboratory was also a careful operation. That - along with high specific activity radioactive samples involved - required one to be especially careful (two flasks of antidote solutions, ready to be mixed together and swallowed, sat on the bench as a precaution).

No problem at all with the right precautions.

Hmmmm... I remember being in a meeting with a plating company about phosphating maraging steel swaybrace pads for ejector-release units on aircraft (underwing bomb pylons) ...

...where I couldn't help noticing a grey plastic container on the edge of a shelf in the little meeting room. It had a big printed label on it declaring it to be potassium cyanide with lots of poison symbols and warning clauses.

The top was on cross-threaded.

I heard the story of a lucky gamekeeper in the days when we often used Cymag to destroy wasp nests etc. Apparently it got damp and filled his vehicle with gas. Story went that he was gassed on opening the door to get in but survived because he fell outside the vehicle...

I was never sure if it was true or myth, but we were always careful with the stuff. At school we were told ‘there are two chemical compounds that smell of almonds - if you smelt it and reached the door, it was nitrobenzene...

A bit like hydrogen sulphide - safe enough while you can smell it (rotten egg smell) but lethal if in cocentrations that deadened the olfactory nerves. I remember we left the H2S generator (a Kipp’s apparatus) turned on over the weekend (fume cupboard turned off). Come Monday nobody was allowed in the chemistry lab until it had been well aired.

Cymag was a very efficient poison, but banned umpteen years ago. I’ve not had any since the middle1970s.

But, let’s be clear, even water can be a very dangerous chemical as well, if suitable precautions are not taken, at times!

I have a recipe for a brew similar to Alan's. It says it boils at 150C or thereabouts, so not only is it caustic it will cause very severe thermal burns. I've never plucked up the courage to try it

Edited By duncan webster on 15/02/2020 22:39:07