I’ve had this happen a couple of times when I used too much lemishine, so I’m careful not to do that anymore. This time I tumbled a bunch of 10mm, setting it for 3 hours when I went to bed last night. Got up around 0430 this morning and rinsed it off. Beautiful shiny new looking brass! I couldn’t leave well enough alone, so after filling and rinsing a couple of times, I filled the tub back up with water and put it back on the rotary tumbler and went back to sleep. When I went to dump the water out, expecting clean water, I had a nasty oily sludge in there. I rinsed it out well again, but my previously shiny brass is now tarnished. No big deal, but I was expecting clean, shiny, well rinsed brass. My guess is that the chlorine content of the tap water reacted and tarnished it. And another thing I noticed is that it seems slicker than the squeaky clean super shiny brass, so maybe that’s a plus.