Grainy surface texture on delft clay cast

[Pickwick]

My first attempt at casting silver with delft clay and I’m cuffed that it actually worked. My question is about the grainy surface texture. Is that just how it is with delft clay, or could I get a smoother surface if I hammer the sand harder (I think I hammered it pretty hard). Also what would be the best type of Dremel bit to clean up rough edges. Thanks.