Corn Cob Filler is made from ground corn cobs and makes an excellent filler for polishing stones. It's softer than walnut shells, providing a wonderful barrier between stones during the tumbling process. Available in a variety of amounts.
Diamond Pacific reminds us that filers are important additions to the stone/grit mix in almost any tumbler or tumbling sequence. Fillers act as a cushion between the parts and aid in distributing grit to stone or metal parts. Filler should compromise around one-third of the load.