Oh, the mysteries of tumbled brass. I began reloading a year or so ago, and chose to go the Thumler's tumbler and stainless steel pins route. I generally tumbled my brass for about 3 hours using only a couple drops (likely less than 1/4 tsp unless get carried away as just squeeze bottle until comes out) of dawn dish soap and the goal of 1/4 tsp limestone (again shake container and hope for just the small amount but sometimes get more). My brass has always come out shiny. I then dump pins through cheap media separator pan over 5 gallon bucket as space is a premium and going the space saving route over a spinning separator. I rinse brass in my sink, then proceed to use my air compressor and blow the remaining water off the brass. I have always been concerned if I get the limestone rinsed off thoroughly.
My dad just gave me a bunch of brass, some likely a good 50 years old and looking pretty much brown in color. I chose to tumble for 4 hours and much of the brass came out looking like new, some with a slightly off color but shiny nonetheless.
Finally, on to the mysteries...
I was given some 7mm magnum cases that were brass, and some that were silver in color, likely nickel plated. I believe these were Winchester cases (others are F-C). I tumbled these between 3 and 4 hours. I followed same procedure rinsing and blowing them off. When done, I separated by headstamp to inventory and pack away as I do not even have a 7mm mag yet. Just hen it dawned on me that I was separating all brass colored cases, not a speck of silver color to be seen. Would these cases have lost all their coating in the tumbler? If so, from tumbling pins, or from limestone/soap mix?
Next mystery..more of a concern. I finished tumbling a batch of 9mm after the family went to bed and decided to simply rinse the brass and let it soak in fresh water until morning, when I would rinse once again and blow it off. (air compressor in garage on other side of wall of the kids bedroom) The brass became tarnished at points of contact with other brass. It looks cosmetic only until use flash to take picture. Did I ruin this brass? Should I be concerned that I am slowly damaging all my brass? Do I need to rinse better? Should we all be concerned with the semi-shine? I plan on using it, but have that little voice going in my head.
I did not plan on taking before/after of 30-30 brass, but took these to send my dad when I thanked him. The 9mm brass is the same, but I moved it to figure out better picture with/without flash and was surprised how different it looked.