Plainsman M390 with 12.5% 48 mesh kyanite wedged in. This was added to improve the drying properties while maintaining the plasticity. However, the throwing also improved! It was easier to pull up into a tall cylinder. The surface texture is only moderately disrupted by a slight graininess.
This is the surface after trimming. M390 is normally smooth. It is plastic enough to be able to tolerate this grog without apparent loss in workability (still throwing well). And it does not feel overly abrasive on the wheel (unless your hand goes down onto the wheelhead). How is that possible? Although the particles of grog are large, they are not touching each other and readily press down into the clay.