My name is Max Goodman, I’m a jewelry designer and educator, and I
run the jewelry studio at 3rd Ward in Brooklyn, NYC
( http://www.ganoksin.com/gnkurl/1b8 ). We recently inherited a large
scale tumbler, along with what I presume to be about a pound of
steel shot. The tumbler is in good shape, and loads from the top.
Having never owned a tumbler before (where I went to school we had
mass finishers, but they all took ceramic media, not steel shot), I
was eager to find out all I could about working with this one. I
filled it with water to about 3/4" above the steel shot, and added
dawn soap as per directions I found online. The first few rounds of
tumbling went fine - because I intend to use this for my lost wax
casting students, I threw in a couple of clean sprues, and they came
out looking shiny - they were silicon bronze. I then put in a silver
ring, and noticed some mild discoloration, almost an oxidizing.
Unsure of what to do, I tried one more piece, and to my dismay the
black tarnish-looking finish increased. I switched out the water and
rinsed the steel shot using a screen, then tried again, to no avail.
Any clues on what I’m doing wrong, or what chemical combo might be
growing this sticky black finish? Thanks!