Black Stains on Brass - Need Help

Andy

Andy

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I picked up a large pile of range brass last week that filled a 4L small-necked jug, and had a quantity of what appeared to be water in it. The brass at the top is nice and shiny, but as you go down towards the bottom, the brass is increasingly stained with black spots that don't rub off, even with 0000 steel wool. Many of the the cartridges have the stain only on the neck, but others are covered pretty well.

So - what is it and what causes it? Brass does not rust (as it has no iron in it), but does corrode. What common situations can cause corrosion (aside from the usual oxidation from the air). Does heat and humidity cause the staining or was something else at play here? The bigger question is: if I didn't care about the cosmetics of it (and I do), would it be fine for use?

I don't mind throwing it into the scrap bin and getting upwards of $1/lb for it, but "inquiring minds would like to know".
 
I've seen pickup brass with dark stains that seem rather durable. They fade when tumbled but do not disappear. Chemical cleaning would probably eliminate them. It is my opinion that they are cosmetic, and have nothing to do with the usability of the cases. Cases which I have seen which were obviously corroded had an etched, roughened texture. My primary concerns with range brass are lack of consistancy because of mixed origins, and uncertainty about the rifles in which the ammunition was fired. Over the years, I have acquired cases fired in currently issued No. 4 rifles. It is remarkable how much of the brass must be culled because of incipient separations resulting from really generous headspace.
 
Thanks. I'm going to try a white vinegar bath followed by a long tumble in corn cob with extra cleaning agent. I'll see if that removes the tarnish. My gut feel is that the brass will be fine for use and that the black is a cosmetic, not structural blight.

I'm with you on the range brass comments. ;) This is all once-fired as its owner does not reload.
 
Maybe phosphoric acid would be in order; at higher concentrations, acetic acid forms an acetate with the copper in brass and can lead to brittleness in cases where hydrogen hasn't been correctly purged off the alloy metal.
Phosphoric acid is gentler and acts faster.
I think that common store-bought C.L.R. is just that.
PP.
 
Update 1

I soaked three that were in varying degrees of tarnish in pure white vinegar, and the black came off in less than 30 minutes!

Leaves light brown spots that should tumble away nicely.

I love success! :D
 
I know this is a 3.5 year old thread, but my first batch of reloads are starting to take on a mottled appearance. Rinsing with water and wiping with a dry cloth does not remove the stains.

I used RCBS lube when resizing, and wiped each with a dry cloth after to remove the lube. The pattern of the mottling somewhat resembles the spottiness of the lube after the case was rolled on the pad...
 
Clean with citric acid. Citric acid is used as the main ingredient of citrus flavoured drink crystals. Buy the kind that normally requires sugar to be added.
 
A Lazerus thread (back from the dead)!

Soak in 50/50 vinegar/water for 10 minutes, rub clean with a cloth, and then rinse thoroughly in clear water.
 
That stain is actually caused by the reaction with grass. Brass in the bare areas was still shiny and the stuff in the grass, was a covered with black stains.
 
tigrr said:
That stain is actually caused by the reaction with grass. Brass in the bare areas was still shiny and the stuff in the grass, was a covered with black stains.
Click to expand...

I've found the exact same thing. Grass clippings stuck to casings that were stored after being collected from damp ground. It usually takes a couple of cleaning and reloading/firing cycles to dissapear. I only reload for personal use, so I don't care too much about cosmetics.
 
i agree about the grass theory buy thats not the only thing that will cause this to happen. ive had cases which have had no contact with grass or outdoors for that matter and the same thing happens. i beleve it to be inconsistancy in the brass much like carbon pockets in steel, which are first to show signs of corrosion, these cases must have "pockets" of lower grade brass which corrode quicker, or first rather. there also has to be a chemical reaction with the burning or burnt powder because i have observed much more of this corrosion on fired brass. my 6 cents,

lannard
 
I had a bunch of range brass that I picked up on the weekend, tried the vinegar trick and it worked amazingly!!! There were some that were really bad and came up really good, now they just need tone tumbled!
 
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