Began using wet tumbling and stainless steel pin media a couple years ago. I agree with lots of previous posts concerning its pros and cons versus corn cob and walnut. I generally like it and it's becoming less cumbersome the more I do it. I usually use Simple Green and the recommended dose of Lemi-Shine and it works just fine.

I've noticed that nickel plated brass loses its bright silver sheen and comes out more like a pewter with an almost bluish sheen after wet tumbling. I've been dumping "regular" brass cases in with the nickel plated routinely. The nickel plated brass is plenty clean and the discoloration, or "new" coloration, does not seem to adversely affect it but was wondering if others had noticed this too?

I am concluding the relatively acidic bath water is slowly leaching the nickel plating off the brass?

I cleaned once fired (with black powder) nickel plated Starline 45 Colt cases with SS pins and Cascade Powdered dish detergent and a bit of Lemi-Shine.
I could see faintly the brass showing through the nickel plating.

In the future I will clean nickel plated cases with a more gentle method.

Sounds like you may be using too much detergent or possibly tumbling for too long. I use a tablespoon of "Totally Awesome" citrus cleaner and 1/4 tsp of Lemi-shine, and tumble for about 2 hours. My nickel brass comes out looking brand new.

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I have one friend who uses the wet tumbling method and I will admit his finished cases look new! To me, it's just too much more effort that I have no interest in doing. I've been tumbling in a corn cob media (Lyman treated Green) for many years and get really descent results. While my cases are not quite as shinny and purdy as my friends, for shooting targets and pieces of paper they are more than good enough.

Stainless Steel pins can and will remove Nickel Plating over time. Solution would be to either tumble for smaller durations or use solid Brass. cartridges. Other than cosmetics, Brass coloration peeking through the Nickel will not in anyway deteriorate performance.

Why would you tumble nickel plated brass in the first place?
All you have to do is wipe it off with a cloth and your done.
Denny

My use of nickel plated cases is more for decorative purposes and to keep green verdigris from growing on the leather cartridge loops of my gun belt.
I think I tumbled the nickel cases 2 to 3 hrs it was a few years ago which was my SOP for brass cases at that time.

I have since learned to tumble standard brass just 1 hour with double the amount of Cascade powdered dish detergent (30ml in 1 liter of water) no Lemi-Shine, SS pins. The dish detergent all ready has citric acid in the powder.

I have also learned that 1 Cascade Platinum dish detergent pod and 1 hour maximum tumbled in my RCBS tumbler will perfectly clean brass inside and out, anything cleans the outside but a product the can actually clean the inside is something special.

The pod doesn’t shine the cases to bright brass, rather it imparts an old gold finish like brass candle sticks. The citric acid in the pod is concentrated so is passivates the metal, makes the cases look like they were painted with shellac, cases look great just not bright like new in the bag brass.
My regular shooting is done with brass cases.

The hard stainless steel pins are removing the softer nickle plating .
Under the nickle is a base of copper ... as these coatings are removed you will see a color change .
Keep tumbling them in stainless steel pins long enough and the nickle and copper will get removed and you will have brass cases .

To answer your question it's the stainless steel pins rubbing/wearing the soft platings off not the lemi-shine in the water leeching it off .

I , personally , only tumble nickle cases in dry treated walnut polishing media ... plated cases come out polished and the nickle stays on a lot longer .
If you resize nickle cases enough this will also wear away at the soft nickle / copper plating .
Gary

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I used Lyman green treated corn cob media for years. I found the cases were slimed with a green tinged greasy film that I needed to wash off. When I learn about the wet tumbling with SS pins cleaning method, I went for it since I had to swirl the cases in a small tub with Dawn dish detergent to remove tumbler slim and dust I was half way to wet cleaning anyway and I had the RCBS wet/dry tumbler. Just need to add a Lyman turbo sifter sieve and small 3 gallon Home Depot bucket and a large baking tray to dry the pins.

I have a question of those that use the wet tumbling cleaning process for their brass? When using two dissimilar metals in the presents of water+chemicals it creates galvanic corrosion of the metals(to what degree?)! When you add critic acid to the water it reacts with the metals(copper, tin, zinc) at the molecular level weakening the metal. How many cleanings will it take to render your brass too weak for use due to case cracking or head separation? I have used corn cob media(unscented kitty litter) with NU-Finish car polish for years. The brass comes out like new and the polish also reduces the dust(greatly). I have 38 nickel brass in my bucket that has been cleaned so many times the Nickel plating is starting to wear off(25+ years).
My .02, jcelect

Thanks for all the thoughts fellas! I was beginning to think the original post wasn't showing up except in my log-ins. I don't generally care what color my brass is and acquired most of my nickle plated brass through friends that pick up at the range for their poor knucklehead re-loader buddy. It does seem the longer the plated brass is left to wet tumble the more discoloration I get. After some exhaustive research it seems likely there is both some mechanical and galvanic processes going on. I may go back to dry media tumbling the nickle plated brass and wet tumbling regular brass or segregating them and running the nickle for shorter periods. I agree with all who claim wet tumbling is a pain compared to dry. Two reasons I'll continue to do it: 1) it's getting to be less a pain as I do it more and gain technique, 2) there is no question it cleans the inside of the cases and the primer pockets significantly better than dry tumbling with corn cob media. I freely admit neither of these reasons may matter to you.

The pewter cartridge color has elicited some interesting comments from my shooting buds so I tell them I buy my brass at Tiffany's now.

Brass and Nickel coated brass are not that dissimilar to create corrosion in a weak acid solution.


Galvanic Series (electrochemical series)

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Still Running Against the Wind

To reduce the time the cases spend in the tumbler getting their mouth dings and soaking in mildly caustic chemicals, I always scrape out the primer pockets with the same tool I used to uniform the pockets.

Sir, you are correct! But the dissimilar metals are brass and stainless steel! Both of these metals are alloys with the base metals causing the problems!
Look at a lead acid battery? The anode and cathode are both soft lead and the electrolyte is a 30% solution of sulfuric acid and distilled water! After the initial charge(specific gravity increased to 1.250) one cell will produce 2.1 VDC. The results to the lead is metal erosion with small particles falling to the bottom of the cell eventually shorting out the anode and the cathode! Dead battery!
jcelect