How To Reduce Ceramic Media Size

How about just tumble them with other rocks in stage 1 and as time goes they will get smaller and rounder?

I've had pieces break naturally because of their flat shape. They got small and flat, and once that process started it seemed to accelerate them unevenly wearing down (probably by getting stuck in the barrel), making them very prone to being broken by rocks during tumbling. I've never deliberately broken them, but I can see the appeal for breaking certain shapes to prevent what I experienced and ensure they move properly in a tumbler.

Breaking so many manually seems time consuming. A quicker way to reduce the size is running them in coarse grit, like pebblesky suggested, especially if you can do it in a rotary tumbler. It will waste grit and media, so whether or not this works for you is really about what you think your time is worth. Is the time it takes to break the pieces with a hammer better spent than the time, grit, energy, tumbler usage, and lost ceramic media it would cost to run them in a tumbler? To avoid wasting grit or taking up barrel space, they could be run with any rocks you are sending through the coarse stage. It will be a slow way to process all the ceramic media, but less wasteful.