Strange that you should get the first load clean and then have
trouble with the next ones. Recently a friend used what she thought
was sterling to make headpins, but they turned out to be
silver-plated copper (from wire, no less...she didn't mark her stock
properly and got plated material among her solid stock). These
headpins caused no end of trouble: problems soldering, problems in
the pickle, problems in the tumbler, before we figured it out.
Once you've made sure it's really solid sterling you are using, I
would recommend using liquid dish soap (Dawn, Palmolive, etc). Just
a drop or two will do.
Sniff the barrel; does it have a sulfur smell? It could be that is
leaching into the solution, especially over an extended use (2hrs as
opposed to 30min). If you detect a smell to it, then I would run
several loads of nothing but shot and liquid dish soap; this seems
to help break in the barrel. (I don't use Lortone, I would hope their
barrel quality is better than the stuff I use, but it won't hurt to
do this if nothing else seems to work.)
Also, the protective action of whatever burnishing liquid you use
breaks down over time. If you are going to use the tumbler for an
extended time, check it, rinse & refresh every so often. At least
until this problem stops.
Without being there and seeing what's going on, these are my best
Hope this helps,