I have been making a bike part for a friend using abs that I would like to give something of a matte finish. I have a vibrator/tumbler unit and the ceramic harbor freight chunks (97027) I was using don't seem to be doing much (although they did an ok job deburring the sharp points). perhaps that's because they are intended for polishing... hmm wish it said that on the container so I knew when I bought it

They are headed off this weekend so I'm looking for another media I can find locally at a hardware store before reverting to scotch-bright pads. Lava rocks, gravel, Any suggestions?