"Sacking" is done by the mason before the mortar is dry. The wall is not cleaned but simply brushed with a potato sack to get the desired coverage. It can be a heavy coat (showing more cement and less brick) or light coat of mortar.
"Smearing" can be applied after the mortar and brick are dry. The mason can apply wet mortar on the face of the bricks with a brush, sponge, rags or by hand using a rubber glove leaving as much brick color to show through as you may want.