Since we are not protecting 'minty luster' like on coins, try a vibratory method with mild abrasive and jeweler's rouge. I use my cartridge case cleaner ( for ammo reloading) which looks like:
Because it is what I have. You can put corn cob media in the unit then put your item in small jar, plastic or glass ( vitamin/aspirin size, anything really that allows it to move around well) with the rouge and perhaps walnut media. Tape the lid.
This keeps your shaker clean and saves you on materials.
If that doesn't separate everything off that is not your item, then you might want to up the hardness step by step until you get results.
