I was planning to clean up some .308 Win brass with my newly acquired stainless steel 'pins' and a rock polisher. I had used it to tumble some of the ANVB (Ain't No Varmint Bullet) tips that j0e_bl0ggs had recently sent, hoping to remove the "matrix" left after they were printed. It worked well enough, but left all the residue in the tumbler. Since he had told me that the company that printed them cleans up their printed objects with a lye solution, I figured I could clean my tumbler up by using a little lye in it as well, while I cleaned the .308 brass.

Using the concentration suggested by j0e_bl0ggs, I put about a tablespoon of sodium hydroxide (lye) in the tumbler and added about a cup of water or so. I added 20 cases of .308 Win brass, sealed the tumbler, and 'let fly'.

It was late - 2345 - and I was going to let it run all night and check it in the morning, but there was some small concern about both the tumbler and the brass, so after 45 minutes or so, I checked. Very interesting!









Pretty interesting to me!

Cleaned the tumbler of all the resin "residue" too.

Paul

I take it the "blued "cases are the result of adding lye and water  to the tumbler.
If that works good, why bother with hot salts bluing?

I think the key is that this is BRASS. No such luck with ferrous material I am quite sure.

Paul

Awhile back, there was a thread about marking cases. (can't find it now durn it)  It would be handy for that.
How durable is that coloring Paul?  
Think it would survive another trip through the tumbler, without the lye??

Of course, these cases are for the .300 Blackout!!!!!!!!!!!!!!!!!!!

QuoteHow durable is that coloring Paul?  Not very at the moment.
Think it would survive another trip through the tumbler, without the lye?? I seriously doubt it.

That said, it might be rendered more durable with longer in the solution. I don't think anything short of paint or powdercoat will be very durable on brass. What makes brass a good material for cartridge cases makes it a poor material for taking a coating in any moving parts - it's soft.

I kinda like the "blacking". I think I'll use it on my 8mm-08 cases. Black cases for a "black" rifle ala Don's comment about the ".300 Blackout".

I think modifying the process might result in a more durable finish.
1) tumble brass without lye to get as shiny as possible or preferred,
2) THEN soaking in water/lye solution until desired "blacking" was achieved.

I haven't looked yet, but I THINK recipes for "blacking" brass are found in Firearms Bluing and Browning by Angier. I'll have a look and see.

Paul

PS - Might try it on some bullets too!

Oh, boy, off again on a new project.
As an aside, it seems the .308 case now has 5.56, 6, 6.5, 6.7 7mm variants, plus the .308, 8mm, .338, .358 and .375 .
Has anyone tried .400 or .416, yet, or is that big going to do away with the shoulder, all together?

Sulphur content, like egg yolks is a common way of achieving a patina on brass, have not come across using a lye solution, looks like a business opportunity for the steam train models makers has arisen...

Must have a bash with it, looks like an easy way to segregate some particular brass!

Hernley's Formulas:


Black Color on Brass

A black or oxidized surface on brass is produced by a solution of carbonate of copper in ammonia. The work is immersed and allowed to remain until the required tint is observed. The carbonate of copper is best used in a plastic condition, as it is then much more easily dissolved. Plastic carbonate of copper may be mixed as follows: Make a solution of blue vitriol (sulphate of copper) in hot water, and add a strong solution of common washing soda to it as long as any precipitate forms. The precipitate is allowed to settle, and the clear liquid is poured off. Hot water is added, and the mass stirred and again allowed to settle. This operation is repeated six or eight times to remove the impurities. After the water has been removed during the last pouring, and nothing is left but an emulsion of the thick plastic carbonate in a small quantity of water, liquid ammonia is added until everything is dissolved and a clear, deep-blue liquid is produced. If too strong, water may be added, but a strong solution is better than a weak one. If it is desired to make the solution from commercial plastic carbonate of copper the following directions may be followed: Dissolve 1 pound of the plastic carbonate of copper in 2 gallons of strong ammonia. This gives the required strength of solution.

The brass which it is desired to blacken is first boiled in a strong potash solution to remove grease and oil, then well rinsed and dipped in the copper solution, which has previously been heated to from 150° to 175° F. This solution, if heated too hot, gives off all the ammonia.

The brass is left in the solution until the required tint is produced. The color produced is uniform, black, and tenacious. The brass is rinsed and dried in sawdust. A great variety of effects may be produced by first finishing the brass before blackening, as the oxidizing process does not injure the texture of the metal. A satisfactory finish is produced by first rendering the surface of the brass matt, either by scratch-brush or similar methods, as the black finish thus produced by the copper solution is dead —one of the most pleasing effects of an oxidized surface. Various effects may also be produced by coloring the entire article and then buffing the exposed portions.

The best results in the use of this solution are obtained by the use of the so-called red metals—i. e., those in which the copper predominates. The reason for this is obvious. Ordinary sheet brass consists of about 2 parts of copper and 1 part of zinc, so that the large quantity of the latter somewhat hinders the production of a deep-black surface. Yellow brass is colored black by the solution, but it is well to use some metal having a reddish tint, indicating the presence of a large amount of copper. The varieties of sheet brass known as gilding or bronze work well. Copper also gives excellent results. Where the best results are desired on yellow brass a very light electroplate of copper before the oxidizing works well and gives an excellent black. With the usual articles made of yellow brass this is rarely done, but the oxidation carried out directly.

Henley's Formulas

Black Finish for Brass
I

A handsome black finish may be put on brass by the following process: Dissolve in 1,000 parts of ammonia water 45 parts of natural malachite, and in the solution put the object to be blackened, after first having carefully and thoroughly cleaned the same. After letting it stand a short time gradually warm the mixture, examining the article from time to time to ascertain if the color is deep enough. Rinse and let dry.
II

The blacking of brass may be accomplished by immersing it in the following solution and then heating over a Bunsen burner or a spirit flame: Add a saturated solution of ammonium carbonate to a saturated copper-sulphate solution, until the precipitate resulting in the beginning has almost entirely dissolved. The immersion and heating are repeated until the brass turns dark; then it is brushed and dipped in negative varnish or dull varnish.
To Give A Brown Color To Brass
I

In 1.000 parts of rain or distilled water dissolve 5 parts each of verdigris (copper acetate) and ammonium chloride. Let the solution stand 4 hours, then add 1,500 parts of water. Remove the brass to be browned from its attachment to the fixtures and make the surface perfectly bright and smooth and free from grease. Place it over a charcoal fire and heat until it "sizzes" when touched with the dampened finger. The solution is then painted over the surface with a brush or swabbed on with a rag. If one swabbing does not produce a sufficient depth of color, repeat the heating and the application of the liquid until a fine durable brown is produced. For door plates, knobs, and ornamental fixtures generally, this is one of the handsomest as well as the most durable surfaces, and is easily applied.
II

A very handsome brown may be produced on brass castings by immersing the thoroughly cleaned and dried articles in a warm solution of 15 parts of sodium hydrate and 5 parts of cupric carbonate in 100 parts of water. The metal turns dark yellow, light brown, and finally dark brown, with a greenish shimmer, and, when the desired shade is reached, is taken out of the bath, rinsed, and dried.
III

Paint the cleaned and dried surface uniformly with a dilute solution of ammonium sulphide. When this coating is dry, it is rubbed over, and then painted with a dilute ammoniacal solution of arsenic sulphide, until the required depth of color is attained. If the results are not satisfactory the painting can be repeated after washing over with ammonia. Prolonged immersion in the second solution produces a grayish-green film, which looks well, and acquires luster when polished with a cloth.

"My" lye solution seems a bit simpler. :) That said, there is a lot of information in the above that suggests ways to improve the durability even of the "lye method". I'll have to give it another go after I get back from looking for caribou.

Paul

Yah only posted that stuff as reference, certainly will try the lye....

On the subject of the 'durability' of this finish:

I took the cases you see in the above photos and necked them up to 8mm using the 8x57 resizing/decapping die. About a quarter of an inch of the body just below the shoulder was forced into the die. There was no removal of the dark patina. In other words, the finish was more durable than I thought it was.

Paul