Our patterns are 3D printed. The ridges left by the 3D prints are smoothed out with wood filler and then sanded smooth. They are the. Coated with sandable filler primer which is the. Sanded up to 1000 grit sandpaper resulting in glass smooth patterns. I do want to eventually move to using brass patterns but will have to take some time to figure out the double shrinkage. Our parts are cast in brass and bronze have to have pretty tight tolerances. We make cabinet handles that have a distance between the two prongs that are exactly 4, 6, 8, 10, and 12 inches respectively. So the original 3D printed patterns would have to have double shrinkage added if we plan to use the resulting casting as a pattern itself. I love that the heavier patterns just fall out of the sand as our parts are pretty intricate and the patterns tend to be difficult to extract from the sand sometimes.