This photo shows the difference between a two-part sand mould and an open pour. The level of detail on the two part mould is far greater than on the open pour.
I had read that this was the case, but I’d not experimented myself previously.
Both pieces are ‘my-smelt’ copper with silver alloy, cast in oil sand. The piece on the right is made in a two-part mould. The piece on the left I heat-patinated after I’d cleaned it up. Both are from the same former, which is an Edwardian mourning brooch. I will make the more detailed piece into a necklace; the open pour piece is too heavy to wear, but is very tactile.